I'd forget the homemade gift, have all the kids participate in making one lovely card which they sign, and then stick a Starbucks gift card in there.
If other mom's will contribute great, but it sounds like you are on your own pretty much so you'll just have to live with either paying for it yourself or with the help of one or two others, so plan on a smaller gift card.
If you're room mom, the gift should be from all the kids, regardless of their participation.
If you're not room mom and you're doing this you get a Gold Star! And again, all kids should get credit regardless of whether there parent is a slouch or not.