The offer I have personally received was a swapout from the HR10-250 to the HR20-700 for $99.00. Others have reported getting the HR20-700 for free. I think it depends on your status with DirecTV and the CSR you get. Some people have claimed that they kept calling back until they got a CSR that would give them the best deal. I only tried once. Good luck.
Since I own my HR10 I have no intention of swapping it. If I feel I really need MPEG4 locals then I'll pay full price, at that time, and hope the HR20 (or whatever the model is at the time) has the bugs worked out. But, I suspect it will be awhile before HD locals are available in my area.
They will give it to you free. Directv gave me a free HR10 in July 06, They upgraded it to the HR20 free and let me keep the HR10 and move it to a bedroom. You might have to call a couple of times - CSR roulette...