Blitz DTT DC2. Monitors your boost and makes it so you don't have to wait 30 sec to shut down your car every time. $120. Next, either get a AWR front motor mount so your car doesn't bounce so much when you spin the tires or start saving for an exhaust or intake. There will be people who tell you to get a boost controller, but it doesn't sound like you have a lot of money to blow so why void your warantee?
Another idea to do with the $80 is go get some high-temp primer/paint (color of your choice), and a wire brush and touch up your brake rotors (I'm sure you see that they are probably rusty and take away from your rims look). Also, some redline MT-90 synthetic tranny fluid will make your shifts much more smooth. Getting some shifter bushings wouldn't hurt. All are pretty cheap mods.