i have one of the grubees just like that but in silver and with cns carb. my cns works great but i think im in the minority. the motor runs pretty well but the exhaust studs in mine were very poorly threaded, had to go to autozone and rent a tap and die set, was $95. i got the money back after i returned the kit but if i didn't have $95 for the to hold on to i was outta luck.
honestly i wouldn't want to use a cheap bike. my worksman was $350 shipped, and gave me tons of head aches (but i think i got it just right atm, and that will be sweeeet). but i'd still prefer it over a cheap bike thats easy to set up. bicycles aren't made for this, so you want to get a bike that will handle it the best, to me its a matter of safety.
i'm not saying cheap bikes are always unsafe, but i don't want to chance it personally. regardless of what bike you choose, don't run a front fender http://motorbicycling.com/f30/motori...ngers-315.html
i realize you're probably on a budget, but later if you get some extra cash, i suggest getting a good bike to switch it over too.
good luck with your build.