The Eldritch Poisoner
The Eldritch Poisoner archetype (from Black Markets) replaces the Alchemist's bomb ability with the ability to create a unique poison, arcanotoxin. This toxin can be created as a standard action and applied to a weapon as a move action (at level 1). It's also free.
At every even-numbered level, you can upgrade your arcanotoxin. Here's an example for a level 13 - Eldritch Poisoner:
Type: Injury; Save DC: 20; Frequency: 1/round for 6 rounds; Effect: 1d6 Dexterity damage; Cure: 2 succesful saves
Discoveries
Normal alchemist discoveries don't alter arcanotoxin. Thankfully, the archetype has some other discoveries you might be interested in:
- Envenom: Allows you to both create your arcanotoxin and apply it to a weapon as a move action.
- Sickening Toxin: At level 12, your arcanotoxin also inflicts nausea on its target.
- Lethal Toxin: Your arcanotoxin now deals Constitution damage.
Other Stuff
- The Potent Concoctions trait can give your arcanotoxin and one other poison a +1 to their save DC.
- The Concentrate Poison discovery is invaluable for creating other poisons, as noted in your previous question.
- The Eldritch Poisoner at this level would have 4d6 sneak attack damage. You can choose to forego the additional damage to increase the DC of your arcanotoxin, for a maximum benefit of +4 to the DC.
Finished Result
After taking these into account, a level 13 Eldritch Poisoner with 20 Intelligence can create an arcanotoxin like this:
Type: Injury; Save DC: 25; Frequency: 1/round for 6 rounds; Effect: 1d6 Constitution damage and nausea; Cure: 2 saves
Results
Poison should work at least 50% of the time against an average CR13 monster (assume base save between 13-16)
With saves between 13-16, a creature would succumb to arcanotoxin 40%-55% of the time. This barely squeaks by your conditions.
Little chance of accidentally poisoning yourself at any point in the preparation or use. (It's obvious, but worth mentioning).
This build is immune to poison, from the level 10 alchemist poison immunity ability.
Poison preparation should take the least amount of time possible <1hr is preferred.
Arcanotoxin can be created and applied to a weapon as a single move action (thanks to the Envenom discovery available to this archetype). Additional mundane poisons can be created using half of the normal time (from the Toxicologist archetype feature).
Poisons should be deadly (=>40% chance of either killing or long term incapacitate)
If the creature's save is 13, on average it will be poisoned for 3 rounds. During this time the poison can deal 3 - 18 Constitution damage. This may not be lethal, but it will do considerable harm. Nausea will prevent the creature from doing much besides moving.
[optional] Poisons should be reusable (the more effects you can get
out of a single dose the better).
A single usage of arcanotoxin is only a single dose, but you can prepare additional doses as a move action. At level 13, you could do this 18 times per day.
In the event multiple paths fulfill all the requirements, the one with the lowest cost per effect will be the accepted answer
And the best part - arcanotoxin is free! Monetarily anyway.
This is a hack in the crafting rules, not in the fabricate spell.
That said, in the absence of a hard rule I could not find, there are two contradictory implications at various points in the rules:
1) It is at least strongly implied that 3.5e coins are pure metal. The PHB, on p. 112, notes that a gold piece weighs about 1/50 lbs, and also that 1 lb of gold actually costs 50 gp. There is no reason to think that the "1 lb of gold" is intended as an alloy, so the implication is that coins are actually pure gold, as silly as that is. (Gold is soft and not very durable in pure form. At the absolute minimum, the implication is that if one buys "a pound of gold" one gets exactly coin-grade gold alloy, which does not change the argument here.)
The same logic holds for platinum, silver, and copper, which is a little insane, but it's a simplifying assumption for a game and it's what the rules say.
2) Crafting, on the other hand, makes a simplifying assumption in the other direction: That materials account for 1/3 the total value of any object. I.e., a bow costs more than a stick and a string, because it took someone time and skill to put it together, leather saddlebags are worth more than a bloody cow hide because tanning is a filthy disgusting process, etc.
This is just as silly an approximation as the coin ratios above, but it is a game and it is what the rules say.
The implications under these two rules, as regards coins, are mutually contradictory. I see no way they can be reconciled. If you are insisting on a strict RAW answer, then, yes, it seems a mage can arbitrage the system, and with far more profitable platinum, even.
As a GM I would disallow this in a heartbeat. (That said, some people might find it interesting to work through the idea of a king or a wizard pumping money into the economy; but that is the sort of genre control I expect GMs to exercise and simply say, "I'm not dealing with that.")
Best Answer
The best resource available is the Complete Cost Reduction Handbook, which can get your crafting gp costs under 5% of the market price, and also covers how to reduce crafting times and XP costs. The best methods are Extraordinary Artisan and Bind Elemental from Eberron Campaign Setting (Exceptional and Legendary Artisan cover time and XP, respectively). Magical Artisan from Player’s Guide to Faerûn is also a great addition, assuming you can mix Eberron and Forgotten Realms material – it reduces all of the above, though less than the individual Eberron feats do. Several guilds from Dungeon Master’s Guide II also can help.
The fabricate spell can speed up mundane crafting immensely. A dedicated wright (Eberron Campaign Setting) doesn’t actually make things faster, but it can craft for you while you’re off adventuring; this is a highly-recommended use of your Craft Homunculus ability. Unseen crafter from Races of Eberron can provide a similar function.
Avoiding the need to find the materials for sale is possible with true creation, but that is quite high-level.
This is extremely powerful, and will break most games, particularly in a campaign where 3.5’s systemic imbalances are exacerbated by less-than-usual wealth. An artificer could easily dominate such a campaign as it is; really pushing for reductions will dramatically increase the likelihood that you’ll become literally one of the dominant forces in the campaign world, long before your non-magical teammates could manage any such thing.