personally i would do an exhaust first, that is what makes a mustang fun to drive. plus it is the most expensive bolt on parts.

you can get MAC Hts coated long tube headers for $350 brand new from www.brenspeed.com, a prochamber or H/X-pipe for $200 at www.rpmoutlet.com, and a cat-back from www.completeexhaust.com for around $320 shipped if you call them.

that will net you a nasty sounding exhuats and you could install the cat-back yourself. then use the last couple hundred to have the headers installed.

but you could always go with everyother bolt-on and have a quiet sounding mustang. or just find a used off road-h pipe then weld in a set of cheap flowmasters and have a $200 exhaust and buy lots of other bolt-ons. its all just personaly preferance to what you want.

gears are an option but it will cost you around $500 for the entire install and gear.