They have only just recently come out with the Elite version of the 360. That's the one everyone is telling you to not get. I'd agree that, for an 11 year old, it's probably not necessary. When shopping, you'll know it's the one not to get because it'll be black instead of white. This can help you to quickly narrow down what you are looking for.
I have had the Xbox 360 version everyone here is suggesting for awhile now. I like it, and it sure is nice having the harddrive and wireless controllers.
I have paid for the online service since the day I got it. It's $50 a year, so like a bit over $4 a month... not too bad really.
Wireless controllers run on 2-AA batteries, and they come with a set. But unless you want to be buying AA's everytime you turn around, you should get the Xbox 360 Quick Charge Kit: http://www.xbox.com/en-US/hardware/x/xbox360quickchargekit/default.htm
which comes with a rechargable battery pack, but is capable of charging two at once. It's a charging stand that you plug into the wall. I have one, and it's much nicer than having to replace AA's all the time. You can pick up more rechargable battery packs for like $12 a piece: http://www.xbox.com/en-US/hardware/x/xbox360rechargebatterypack/
at most electronic stores (Best Buy, Circuit City, etc.). But like I said, it comes with one, so you should be good if it's just your son playing.
As an alternative to the Quick Charge Kit, you could get the cheaper recharge solution: http://www.xbox.com/en-US/hardware/x/xbox360playchargekit/default.htm
It's called the Play And Charge Kit, and basically, it's a cord that you plug into your 360 then into your controller. It recharges your battery pack while you play. Unfortunately it makes a wireless controller effectively wired while it recharges. For some people this is not a big deal. It just depends on the person. It uses the same rechargable battery packs as the Quick Charge kit, and comes with one as well. It costs $10 less, but can only charge one battery pack at a time.
New games almost always start out at $60. But, as was already pointed out, you can get them cheaper if you don't buy them at release. Wait a few months and see what happens. The day-after Thanksgiving would be a good day to plan to buy games. Sometimes they are advertised for as much as 50% off!
Anyway, I've been very happy with my Xbox 360 and would definitely recommend it.