unlimited data is 44.99
4mb data is 34.99 (i think)
If you want to moniter emails and respond quickly, I would suggest the 7290. I had the 7280 and bumped up to the 7290 because of bluetooth.
The 7100g has a qwerty keypad, but it is not the standard that the 7290 has. Each key has two letters, which would throw me off if I was typing fast. The 7100g however has more features than the 7290, but overall in a poll, more forum users cited the 7200 series as their device. see link below Which Model BB do you use
Hopefully this will help. If you are seriously wanting to switch to the 7100g i would break contract, that is just my opinion though