OR, how about all pawn non-tournament games be unrated (not counting towards rating for either player)

For tournaments, let the games against Pawns count towards ratings, but just don't "show" the pawns rating in any list. Let it add up in the background, and if someday that pawn become a paid member, then those tournament games that were already played could then be included in the ratings list.

A pawn would still be able to play their games here, but without paying, they will not know how they stack up!.

(Downside is when joinging tournament for a range of rated players - for example, under 1500 tournament)

Good side - A person could not create a pawn account and just play private games with them to help their ratings.