Although the web doesn't have ANY details about the phone and there's no mention about S7 Edge. So I am not sure what would be the final price of S7. BTW T-Mobile sells S7 for $669.99 and S7 Edge for $779.99 so this will give you rough estimate of MPCS version of the phone.
Since no information is available and it's limited time offer, you have to move quickly.
1. Pre-register now
2. Purchase S7 by 3/18 (S7 Edge not available??)
3. Fill out online form and upload receipt image by 3/31