The best way that I can see you improving your combat effectiveness is through the specific spells you choose.
As you had said, money is sort of tight in your campaign, so you need to make due with what you have at your disposal naturally. Luckily, this isn't hard considering that you have a +4 Cha score (Giving you anywhere between 1-4 additional spells per day at your current bonus). So considering your want to improve how well you do in combat, focus on preparing combat buff spells
These are the spells that I think you should prioritize (keep in mind that I only have the core rule book on hand):
+Bless Weapon(1st): A very situational buff, but powerful when used against the right enemies (ya did good on this one)
+Magic Weapon(1st): Prepare this instead of Bless. Bless may give you a bonus against fear, but Magic Weapon increases your damage as well as your attack bonus.
+Bull's Strength(2nd): I know that you put most of your stuff into Ranged Weapons, but everything on the list available to me is either a buff you don't need or something that seams too underhanded for a "rock star" (also, I don't think you need a spell that lets you take half of the damage that your friends take when there is a fully-functioning tank). As you may already know, Bull's Strength increases your Strength Ability by 4, so at the very least, you increase your Combat Maneuver Scores. This means it's easier to absolutely wreak an enemy's day by affecting how they move, inflicting statuses on them, or simply moving through them.
+Greater Magic Weapon(3rd): THIS is one of the key spells you should prepare when you get into the upper echelons. It's like Magic Weapon, but it gives you additional bonus amounts for every four levels your character has. Also, this spell specifically states that you can cast this spell on up to 50 arrows in the same quiver; this means that if you have to switch to another bow, or if your party also invests in bows, the spell is used to its maximum potential between multiple weapons.
+Prayer(3rd): Anyone in a 40ft radius of you receives a +/-1 to every roll depending on their loyalties; That's an increased advantage of 2 against whatever enemies you are fighting!
+Dispel Chaos/Evil(4th): these two spells give you +4 against the attacks of the designated alignment and automatically dispels effects cast by said creatures or spells that are of that alignment
This last one is just in case you attempt to build physically or your Fighter is being cornered by a Demon or something...
-Holy Sword: PROS: weapon automatically becomes +5 AND deals an additional 2d6 damage to Evil Creatures. CONS: Can only be applied to melee weapons and negates the powers of whatever weapon it is used on (that last bit could be fun to use against an enemy using an all-powerful cursed weapon, but again, this is a bit situational)
I hope this helps.
P.S.: Your party should invest in Heavy Repeating Crossbows once you hit level 10
(source: threadbombing.com)
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Best Answer
I can't find anything besides magic items that do what you want. Nothing else reaches the bar you've set. It doesn't even appear official or 2nd-party feats can let a factotum use guidance of the avatar [div] ("Spellbook" here). Consider adding the spell guidance of the avatar to your spell list so that employing wands of it are easier via 1 level of the cloistered cleric (UA 50) variant cleric; this gets decent skill points, and 3 Domains--or 2 Domains and, with the DM's permission, swap out the knowledge Domain (as per CC 52-3) to acquire the feat Knolwedge Devotion (CC 60) that way rather than spending your level-up feats.
Magic Items
These are listed in their possibility of approval. They start reasonable and get progressively more shady. Steel yourself for fights and recrimination if drawing from the bottom of the list. I am only presenting the information; the DM must determine if and how the following function in his game. Omitted are even more obvious sources of acquiring spellcasting (e.g. a minor ring of spell storing (DMG 233) (18,000 gp; 0 lbs.), an ioun stone (vibrant purple prism) (DMG 260) (36,000 gp; 0 lbs.))
The Spell Itself
I can't imagine a class that wouldn't benefit from being able to use the 2nd-level Clr spell guidance of the avatar [div] ("Spellbook" here). However, it's author might have a different definition of what makes a balanced spell than other writers do. The only other spell contribution the author's made that I can find is the spell dirge of discord [ench] ("Spellbook" here), which in the link is a 5th-level Clr spell but was overhauled in Complete Adventurer on page 45 to a 3rd-level Brd spell (the updated version changes the original spell's ability to give affected creatures a -8 penalty to Dexterity to a more reasonable -4 penalty to Dexterity). Also, the spell guidance of the avatar is 3.0 material, making it suspect at some tables, and wasn't included, like many older published-first-on-Wizards-Web-site spells were, in the Spell Compendium. It's an orphan spell, existing solely on that page, a relic of a past edition, never officially referenced again. In short, don't marry it yet--even a reasonable DM might not allow the spell guidance of the avatar into his game.