secondly you need to decide on a class. there is j, clubman, rotax, 125 gearbox etc. i race j class which is the cheapest but isn't really that much slower than the others. it is also the easiest to set up, has the simplest engine/carbie for tuning etc.
the best brands are arrow and top kart. personally i like top kart. a good j will set you back 2-3 grand second hand or about 5 grand new. you will also have to check if the engine has been blue printed or not. it has to be done so if it hasnt it will cost between $800 and $1000. also tyres are about $500 a set. that does it for a basic cart set up to race.
you will also need a helmet, gloves, suit, boots. the helmet you can get any one you like but the rest will cost about $800
your license will set you back i think $350. it costs me $282 to renew it so it will cost you a bit more than that to get it the first time.
all up just for a second hand kart and equipment (excluding helmet) and license you are looking at between $5000 to $5500. and for a new kart between $7000 and $7500. on top of this there will be the fees for your club membership etc. there are also other small amounts here and there but this is the big chunk of cash needed (as long as i haven't forgotten anything).
the last thing you have to consider is how you are going to transport it around. they don't quite fit in the back of a ute unless you take off the back tares so most people just get e cheap trailer.
if you have any other questions feel free to ask away. if i think of anything i have forgotten i will add it later.