Appendix in TOC

I do a lot of documents that have Appendix. Standard formating for these documents is letter then page number for each page. Every time I update the document (shift A then F9) I have to add "A", "B" etc. to the TOC. Each appendix has a section break before it so it has it's own numbering. How do I add text "A" to a page number field code so I don't have to do this every time? And I don't want to have to reformat some heading and add new number styles. I was hoping I could just add to the field code in each appendix section.

Thanks.