If you're making a portable you probably need something to watch it on. (Unless you want to guess what's happening in the game, but I wouldn't advise that) Anyway, this forum is your "Hacking a pocket TV/screen" one-stop solution. Share your experiences and knowledge here.
Dixons has a couple of 2.5" tv's around the £50 mark. Saw some over the weekend, was surprised at the cheapness.
Alternativly (if acceptable) you can get a 3" tv from ebay for aroung £35ish. The casio ev-680, bought one the other week, looks like a nice piece of kit.
Didn't know you get them in the u.k. might be worth a thought for any later projects. But to me, size is everything so i will be keeping my screens as big as possible.
When you have finished your project, please post pics, lots of them, i am thinking of making something similar.