I expect it'll be free otherwise how would Internet Recovery know what you're entitled to? If they're moving to the iOS model, we'll see annual major releases and it'll deprecate hardware faster than before.
I've installed Lion on a pre-Lion macbook pro 2010. Recently they've released update for it so that it support Lion Recovery.
Now, I tried to use Recovery to install Lion, and I was asked for AppleID details of the account with valid Lion purchase on it. It didn't want to install otherwise.
So no problem checking entitlements...