I played on Party when they allowed US customers, and the fee was always a dollar for there $5 SNGs and MTTs. They use to state the fee separately.They think people will notice or care less not knowing.
However, some sites due charge a larger fee for the smaller SNGs and MTTs. Poker Stars
charges a $.20 fee on their $1 SNGs, but only $.10 on their $1 MTTs. Pitbull Poker have the highest fees of any site(on SNGs). They charge a $.05 for a $.10 SNG.