My dad suggests pvc piping and making my own cai, but id rather get yalls opinions. What about exhaust? What are your recommendations for cat-backs on a 94 Celica GT

I went with a custom 2.5 inch catback exhaust from a local shop. Thats the best way to go unless you want to buy a Greddy SP2. As far as the intake, just buy the one from ebay for a 90-93 Accord. Thats the easiest way to go unless you really want to go with making your own. I really wouldn't recommend going with PVC though.

i got my injen CAI off nopi, or you can just got to injen.com mine was only $136

I did some more reading. PVC isnt too favored so I figure I'll buy one off ebay. As for the exhaust, where can I buy one to put on myself?

Go on some reputable sites and buy a muffler you like and take it to an exhaust shop. A lot of guys here buy Magnaflow mufflers and have an exhaust shop fabricate the piping for it. Magnaflow, HKS, Vibrant Performance, etc.

Oh so a shop will make your exhaust from whatever muffler you bring to them.. kk

A shop will make the piping in which ever size you choose. Whether its 2.25 or 2.5 they will make the piping and then which ever muffler you buy will be attached to the piping. But yes, most people go with Magnaflow, Apexi N1(style), HKS, and others for their muffler.