Originally Posted by Rev.Chuck

Beware the 18" wheel bicycle, the tires and tubes can be hard to come by.
You will need to bump your budget if buy from the LBS, at least $160 and probably around $200 for a true BMX. But the bike wil be assembled,and there will be service after the sale.
AND
Is he looking for a BMX or do you just want a simple bike(one without gears)?
What is his inseam? This is a bigger factor for fit than his age.

My recommends:
for the money: Giant Frantic or Specialized Hotrock 20" $160ish These are really what you are looking for.
More money, tougher bike: Giant Modem or Rhythm, Specialized Fuse, or a Redline Raid