Bike shops aren't problem-proof either. When I bought my gf her Raleigh, I had to take it back a couple of times for some derailleur installation problems. One of the wheels had fallen out of true, even. The mechanic just made up an excuse about how many different people assemble the bikes and that I didn't need a wheel trueing.
Yeah, right. They assemble the bikes right in the shop!
So I ended up truing the wheels at home. Good practice.
Anyway, back to the first question. I got my bike for $172 on eBay, used '91 Trek 7000 aluminum bike weighing less than 30 pounds (haven't weighed it yet, but feels hella light!
). If I were you, I'd go on eBay and get a used bike. Don't worry about components because all components fit all bikes, regardless of the frame size. All bikes are upgradeable. There are very few exceptions to this, and usually that's because the bike's REALLY old, like 30 years old.
Usually, if the bike's a high-end bike, it'll come with quality components and it'll give you some good times before you have to really start spending cash on it to fix it. It may need some maintenance, but nothing that'll break your bank. A new chain costs less than $15 now.
Since you are posting on this board, I figure you are experienced enough to know what bike's a good bike, so even if you find a Walmart bike that's got a good frame, remember: components can be swapped out!!