i am planning to build a go kart and do not know what engine to use, i have never built a go kart or motor bike or anything. it would be useful if you could get a few different options based on cost (for example a $300, a $500 and a $700, i would like to know a good but low budget engine). I’m not into competitive racing, i just want to build this for fun and experience. i live in Victoria so i need one i can get easily. Thanks

Best bet is to take an old dirt bike engine, around a 125cc 2 stroke.. Run a clutch and a hand shifter.
Your going to be infinitely more happy with this, and if you shop around you can get one alot cheaper than a normal horizontal shaft engine with a centrifugal clutch.
nothing as fun as 20hp and a clutch in a little go-cart