if you're just going for a bike to mess around with hobby-wise, a cheap bike is ok. that way if you get bored of it you're not in too deep, and if you get hooked, you can make all your mistakes on that, then build up something cool.
but if you needed it to get to work or school everyday, better buy a bus pass with the money you save on the bike.
also, when done right, the china engines can be pretty reliable. depends a lot on your knowledge of how things work, and your MacGyver skills. on my main rider, i've got about 9 months on it, and at least 5000 miles, and it's still going strong. i'm not saying nothing ever went wrong on it, but nothing i couldn't fix. and if it failed today, i think i got my money's worth.