Do a search for "trd exhaust". that should bring up a quite a few in-depth threads that this has already been discused in. Floating around here somewhere is a thread that someone took the time to make an exhaust-compilation video file. So you can listen to the different exhausts back to back.
But ya know what, most people don't know how to search, and I'll just go ahead and assume you're one of them--don't take it personal. So I'll just upload the vid to my server. One sec.
http://lindhome.com/photos/tc/exhausts.wmv
There. It's 3am, and I'm feeling generous for some reason. Just watch the video and make up your mind.
At any rate, the best investment I made for my car was buying a V1. It has "saved me" money so many times.. It's a good "investment". But there are plenty of people here that wouldn't consider that a "mod". If you've only got $200'sh.. maybe get some tint? I can't think of much you can get for $200. If you can't make up your mind, I'd say save the cash, and re-think your upgrades when you have like $400 or $500. Then you can look into exhausts, springs, fog lights, different front grilles, struts/shocks, HID's, brakes, sound-systems... the list goes on and on and on.