Help! I'm being held hostage.

Help!  I'm being held hostage by prepaid cards.  It used to be "Mom, can I have a dollar to get some candy?"  Now, it's "Mom, can I have $20 to get a PS3 card, or an iTunes card, or a Roblox card...."  Thank goodness he hasn't discovered prepaid VISA cards!

Now before anyone thinks I don't give my son anything - perish that thought - I do indulge him.  He's an only child.  We have very few kids in the neighbourhood to send him out to play with.  So, yes, he spends too much time on his computer, and on the PS3, and on Roblox, and playing with Lego, and playing the drums, and beating up the heavy bag that's mounted on a basement ceiling joist and shakes the whole house when hit.
I'd love it if he would take to a sport, but the competitive spirit gene seems to have skipped his DNA.  It's hard to accept for me, as I grew up in a household where breakfast was a competitive sport. :)
He's not even a teenager yet.  I dread the day he has a license to drive.  I'm sure I'll hear "Mom, can you spot me $100 to fill the tank?"
I love him to death. And he loves me.  And sometimes I let him get away with manipulating me.
It's a "Mom" thing.