The Pandaboard looks like a good fit, but the instructions to install a Linux distro are a bit scary . I guess I could do it, from my Mac, but I'm a bit afraid to mess things up with the low-level disk utilities.
Does someones sells SD cards with a distro pre-installed? Or an equivalent device with an easier setup?
If not, there's probably a market for that...
He has plans starting at $5/mo but you'll want to take notice of the of the monthly transfer limit. The $5/mo plan is 10GB transfer a month (which will come to 5GB in/5GB out if you're using it as a proxy) so you won't want to tunnel video or downloads through it. If you go for the $8/mo plan though you can get 40GB data transfer.
I've never had an account with him so I'm not sure if there's a way to check how much of your data allowance you've used for the month. Someone else might be able to chime in about a program you could run on the server to notify you when you've reached a transfer threshold.