Do SF-424As for all sub-awards count against the 50 page limit for the appendices?
No, the budgets should be completed on the SF 424-A form, like the one you will use for the overall project budget. The SF 424-A budget forms will not be included in the overall page count for the appendices (see guidance in the Content and Form of the Application, under the Appendices section, bottom of the 36th page of the funding announcement).