There are several mods under $500 that are worth the money.

1. 15-17% pulley.
2. IE Fixed Camber Plates
3. New tires (close, but not really under $500)
4. Koni FSD shocks ($625)

 

faer,

I asked the Mini techs about upgrading my clutch as well... they all said dont bother. I am friends with one of the techs who has a highly modified Mini, and he has an upgraded clutch. the thing to watch out for, is how sticky it will be! the "upgraded" clutches will be MORE grippy, which if your launching at hi rpm, great; but if your just cruising in the city, its a super PITA. there is very little "play" or give to the clutch... go too strong, and its all or nothing!

also, be aware that messing with your crank pulley will mess with the other pulleys... the main one to keep an eye on will be your water pump; these tend to "go faster" when you have a pulley installed...

 

A lot of people have done the crank pulley and like it... However, there are MORE than just a few people who blew their engines and they all had lightened crank pullies. There was also a time where catastrophic engine damage was directly caused by it..
I almost got one but I chickened out lol I'd like my motor to make to at least 100k
But it's your choice...
Also some drag places won't let you race without a crank damper...