If you're not "well off " then I'd suggest to start with the bbk, then go from there, to the exhaust etc. That's how I'm doing it at least. I found my kit at scoorertronics for my LC (google it, google can be your friend) and it's just a cheap street kit. There's some at racingplanet also, better selection. Zombie would know way more, he's been holding my hand through my building so far.
Honestly, what I've been told is that you get what you pay for. I will soon find out. So if you have faith in building it and the cash then you could have it made!
Also, check out the stuff zombie posted to my thread about the 70cc LC kit installation tips when you get going. He's a damned genius.