You can get them for well under $100
I don't know what the above one is like, it's just to give you an idea.
A cheap pre-paid phone
A cheap notpad (second hand, my DS's first computer was second hand, we cleaned it up and he didn't know the difference)
My own ds isn't to guns ,he's not a gun person, he has a Nerf water gun, but never uses it.
skylanders, wouldn't bother, my ds had the first series, it was a fad with him - lasted about a month (plus you've got keep buying more stupid models!).
Lego - I know you said he has loads, do you mean the normal lego? if so, has he tried technic lego ? My ds loves Technic more than the normal lego.
both my ds loves.
Roller blades, or roller shoes?
hobby building kits ( such airfix models) ?
if he doesn't play any music and likes music (?)- a cheap d*ck Smith type keyboard and learners book? ( Mods- I love the way poor Mr smith's Christian name automatically gets changed with an an asterisk! lol)
woodworking tools and kit?
Hate to mention this one , but I will because it's what many kids are really into at the moment- Minecraft ( I'm trying to get my son away from it, too addictive! He's been banned off it quite a few times by me - I hate the damn thing!))
I'll be buying a canoe for mine this year (his birthday and Christmas are close together) and some more lego.
Hope that helps