3k at level 8 is abysmally poor.
I can see why your PCs are clamouring for wealth, it's not vanity, Pathfinder is balanced around wealth being used for magic items for survival so they are going to be struggling to survive.
If they are point-buy-20 or higher they should have over 66'000gp by this point.
Things you are going to have to do to reduce the difficulty:
Limit high crit weapons
As you play the game longer and longer the chance of any player ever getting hit by a crit goes up to something like 80% (this is ever being hit, not any single chance). Also, critical damage can go up hugely as well. As you have been so stingy they cannot afford anything like a Buffering Cap you must never have weapons with 3x crit range and ideally no 19-20/2x crit range either. They aren't going to be able to take a critical hit and you have left them no opportunity to protect themselves.
Limit weapon damage
Because you haven't left wealth for things like Shawl of Life Keeping to give a buffer for general damage loss you need to dial things back a lot. If game guides would suggest enemies armed with greatsword (2d6), arm them with something like a Longsword (1d8) instead.
Makes things close yet environment to your PC's advantage
The utter lack of wealth of course is going to limit PCs ability to extend the range of their attacks, for example Rogue could never afford Assassin's Sight, so you're going to have to keep things a lot closer yet leave plenty of leeway for your players to disengage or use a height or cover advantage. They are going to need it.
Nerf enemies' stats
Your players should have been able to afford items to boost their core stats by now but obviously cannot. So knock a few points off enemy NPC strength and constitution. Or at least impose some limit like they've been fighting and are lower HP already or are suffering from a disease, tired from travelling, their weapons are damaged or are inherently intimidated by the PC's combat prowess (see sickened, fatigued, broken and shaken respectively).
Still, all is not lost, there's still a lot of very good cheap stuff out there that I can recommend that will be appreciated despite their low cost.
This very cheap item can be hugely appreciated should they be in fear of falling.
Ammunition can be enchanted in groups of 50, so individual units of ammunition would cost 1/50th of enchanting the lot. This can be a great way of cheaply handing out single use bonuses such as Bane Bolt/Arrow against a particular troubling enemy type.
Another cheap item of huge use IF you are a generous GM and give opportunity to use it such as flat roofs nearby that with contracting rope they could quickly get up onto.
Short of being able to boost their Constitution or have a magic item buffer their HP, this will have to do for the big fights. This allows them to stay conscious but staggered when they go to negative HP and Troll Oil stops the steady tick-tick loss of HP when reduced to sub-zero HP.
Very cheap item but gives a considerable buff to protect them from being grappled.
A cheap poison with a very useful effect in how since it requires two saves to end the effect it always works. If your PCs are worries about self poisoning then Blackfinger Paste can cover that concern.
Low CL Potions (50gp+)
There are many 1st level spells which are really good but hard to get out and are viable even at the absolute minimum caster level.
- Touch Of The Sea: can make up for inability to buff stats to be a good swimmer.
- Enlarge Person: is a 1 Round to cast but as little as a Standard action to imbibe
- Blend With Surroundings: great for your rogue when he gets into a pinch.
This is a really good way to give your players the edge in the long run, especially if you are unwilling to drop high value items.
Be generous with traits
This could be a houserule or just a favourable interpretation of the rules but one thing I do is allow players to get a new trait every level and ignore the limit on how they cannot have more than one trait per "list". Considering there are over 1000 traits and normally players can only pick two of them at the beginning of the game that makes this a rather untapped resource.
It can reflect how the PCs have been developing as characters in acquiring new traits. This can do a huge amount to help keep them viable despite such a paucity of wealth.
The unchained rogue talents Minor Magic and Major Magic only grant spell-like abilities, not spells proper nor spell lists, and spell-like abilities don't interact with the spell lists except, for instance, like in these cases, to limit the spell-like abilities the rogue can pick.
The FAQ says:
Question: Does a creature with a spell-like ability count as having that spell on its spell list for the purpose of activating spell completion or spell trigger items?
Answer: No. A spell-like ability is not a spell, having a spell-like ability is not part of a class's spell list, and therefore doesn't give the creature the ability to activate spell completion or spell trigger items.
Thus a rogue without a spell list from another source must usually employ the skill Use Magic Device to activate wands.
Best Answer
There are three other ways I know to increase intelligence.
The first is to convince/bargain with a Succubus to grant you a profane gift; this gives the character a +2 ability bonus to an attribute of their choice for as long as the Succubus wants it to last.
The other is to be old. Aging effects include intelligence, charisma and wisdom increases, middle, old and venerable age giving +1 to each mental stat for a total of +3, But this has a str/con/dex attribute loss. (My emphasis below)
The third is to become a Lich; which gives a +2 untyped intelligence modifier on it's template.
So with these three it's another +7; so without Tome/Wish stacking you have:
20+5+6+5+2+3+2 = 43, close!
Note: If the character were a sorcerer and interested in maximising Charisma then the spell Genius Avaricious could be used as well.