Nice project mate, would be nice to see a little bit more work put into the software, because as far as I can see in your picture the guages are a bit stretched and look kidda out of it. Other than that it looks beaut.
Oh, ok then
you could possibly get away with using 1st gen iPads. would be much cheaper if you can get them...
IPad 1 and iPad 2 are the pretty much the same. All apple do is release a product with a brush aluminium back and then a few months later release a another one that is the same thing but with a gloss plastic backing that is a bit thinner and lighter.
As for jailbreaking, its a very simple task that can be performed on either the iPad 1 or iPad 2 in about 10 minutes, so that really shouldn't be too much of a problem for potential buyers.