I am going to need to buy my son a bike, but don't want to get overwhelmed with facts or pricing. I can't afford $100, much less $3000 for a bike. I think he'd rather have a mountain bike than a racing bike, although the reason for me buying it for him would be so he could cycle whilst I skate. I'm not opposed to him owning 2 styles for different purposes, however. I'll find a place to cram 'em into my living space, if necessary.
What are some obvious pros and cons about buying a cheapie from WalMart vs. a nicer, 2nd hand one?