with the abundance of 5-speeds out there, you're much better off getting a different celica. a transmission swap is feasable, but i wouldnt attempt it unless you have REALLY good connections with a mechanic that will do it for less than $1000 labor, and roughly 1000-1200 in parts assuming you find them all used.
no disrespect either, but i did my transmission swap on my camry when i was 19, and i did almost 6 months of research before i bought the first part. you being 15 and all, i really hope you are resourceful, patient, and persistant. not to mention, you'll need the blessing of your parents, to see if theyre willing to most likely void any warantee that may be left on the car.
if you want further info, i documented my tranny swap:
http://www.tt-cc.com/ratko/swap