I redid the transom in my Seafarer. Are you planning to do yourself or hire out? My father and I cut out the old transom and installed a new one and made the cutout transom into a full height. I also added a bracket.
I had a couple thousand in supplies (coosa board, epoxy - west system, 1708 and assorted fiberglass, fairing compound, etc.).
If you are somewhat handy, it's not a bad project. The worst...for me...is grinding the fiberglass. I'd highly encourage a Rockwell vibratory tool for making quick and precise cuts. You can checkout videos of my progression on my You Tube page here:
https://www.youtube.com/playlist?list=PLKY3HuZDoWwR_iSbBmZmWEkSuhFlgBwjb