Whats about the good old T-Mobile G1 aka HTC Dream?
It will also run version 2.0 and have the same features
1. Should be cheaper than HTC Hero
2. No modified Android UI that could cause trouble or incompatibility
1. Less Rom/Ram
2. Cam just 3.2mp instead of 5mp
I would say as a device just for excersises the cons are irrelevant
and the pros outweigh them considerably.
If you want to dig deeper into the android system the Dev Phone
could be an even better choice. And maybe there are some special
price conditions for educational purposes... at least i think there should
be.. after all you train the app developers of tomorrow