There's a reason people say "do your research". I didn't know anything about anything when I first joined RC ( I still don't, really )I asked questions that now appear pretty silly to me. Pretty much everything you will need to know is on this website, if you do some reading, you will find the answers to your questions. Seeing as I've taken the time to write this, I may aswell throw some numbers out there. Since you have an AE71, if it's a manual then all you will really have buy is a 4AGE which could set you back $500 or it could cost $1500 depending on condition and choice of engine (16v, 20v, GZE etc) With almost all of them you will have to convert it to RWD. Going 20v is a bit more costly too.. And you're going to have to pay for a mechanic's labour which is going to be costly aswell.
In future, do some reading. There are some really good write ups on the 4AGE engines and how to put them into E7's. And maybe ask a few import wreckers about pricing on engines, gearboxes etc. Also talk to a mechanic to see what the cost of labour is going to be, That way you can grasp the concept, be the one asking the questions.