If you're only buying one rare per person, I'd say make it a +1 weapon. They go for $2-3, and the faster the critter dies, the fewer swings it gets at you.
And all things equal, if cash is a limitation, go for quantity over quality.
A +2 weapon (ultrarare) runs about $100. A +1 weapon and Girdle of Ogre Strength (adds another +1 hit and damage) does the same thing for $10-ish.
You have almost 30 slots for tokens. You'll have a stronger character if you have something, anything, in a slot than if you sink all your cash into one token, no matter how super, with 20-some empty slots.
With 100 tokens, you'll have options. But remember, about a third of them will be gold, gear and other less-useful things. And the packs are very, very random. ive opened packs with both uncomons the identical shield, and I remember one that had nothing to wear - no weapons, armor, potions, just gold and ducks and things. (But I've opened hundreds, you probably won't be so unlucky.) People will be happy to trade for them, but that takes time. You won't have any of that to run find people between sign-in and run time, unless you all show up very early.
Not trying to scare you, just setting expectations. If you don't want to buy any extra, you should be ok, even though your average party member will only have a weapon and two to four wearable tokens.
But remember, you're talking to a bunch of people here who love tokens and have a kit with a token in every slot and then some, me included. We have a hard time imagining wanting to go into the dungeon without an optimized outfit, whatever "optimized" means.
"Ceci n'est pas une pipe" - Magritte