As it stands Crosby is signed to the practice squad, not to the active roster.
The Rams will undoubtedly call him up for the Ravens game, but they can do that without signing him to the 53 man roster. In fact, they can do that three times.
"If a practice squad player is promoted to the active roster, he earns the prorated minimum salary for a player with his years of experience." [
www.nbcsportsphiladelphia.com]
So if the Rams promote him three times they would pay him 1/18th of the minimum salary for a player with 16 years experience each time. For player with 7 or more years in the league the minimum salary is $1.65M, or $275,000 for those three games.
Them of course, the Rams would have to sign him to the 53 man roster for the final two games. Whatever the deal is a that point he will only collect two more paychecks: whatever the deal it is it isn't going to break the bank.
AlbaNY_Ram