The developer page has posted the a470 as Magenta so this worries me a bit as the port of CHDK is in beta. Should that worry me?
Not really. The labeling of cameras as beta or not is not very consistent. Basically it just means the port is new. In some cases a few features are missing or not fully tested, but the same is true of some non-beta cameras. The a470 is probably about ready to lose the beta tag.
From a CHDK hacking perspective, the choice of camera doesn't matter too much. I'd go for a digic III/IV camera with dryos, but that includes everything vaguely recent. Even this doesn't actually matter for most things, but if you were to help someone with development for a new camera, it would be more similar than an old vxworks cam.
I'd suggest making a short list of cameras that are CHDK supported, in your price range, and include the photographic features you care about, and then posting that here for feedback. If you don't care about photographic features, then just pick whatever is available and cheap (but if you aren't interested in photography, you might have more fun hacking something else!).
If you are reasonably skilled in C and some flavor of assembler, getting a camera and porting it is also an option. There are also some cameras partially ported that you could contribute to. You can always check out the CHDK source tree, look at
http://chdk.wikia.com/wiki/Adding_support_of_a_new_camera and the other developers pages, and decide whether it is totally over your head.
