Let's see. We have 20 people to arm, correct?
They're probably not proficient with more than simple weapons. Half could be armed with morningstars, a fairly cheap weapon with a high damage (but still allowing a shield). Let's call these the Venus squad for now. The other half could provide fire support with crossbows--half heavy, for damage, and half light, for speed. Call this the Green squad for now. That makes the cost for weapons (10*
+(5+50)+(5*35), or 80+250+175, or 505 gp.
Armor is rather important. The Venus squad should have good armor, say chainmail, plus a heavy wooden shield each. Green Squad would be better-served by mobility, so leather armor would be better. Also throw in a buckler for a little extra defense. Thus the armor cost would be (10*150)+(10*7)+(10*10)+(10*15) or 1,500+70+100+150 or 1,830 gp. If we reduce Venus Squad to scale mail, we reduce the cost by 1,000 gp.
Finally, we would need light. For durability, nothing beats an everburning torch. Unless someone can cast Continual Flame. In the first case, giving an everburning torch to each group of two would cost 1,100 gp, while doing the same with Continual Flames costs 500 gp. So, use the spell if we have it.
Assuming that we buy everburning torches and outfit Venus Squad with scale mail, that costs 505+830+1,100 or 2,435 gp to our party. There's what, half a dozen of us? We each pitch in 410 gp, that's enough to cover miscellaneous costs too.