OK, so I finally get Bebo to work on the Hondo after finding the bad foam outside the stringers (previous thread), and now we find that the left side stringer is rotten where it ties into the transom

. On top of that a small part of the transom is rotten where the stringer ties in

We also took out part of the glass from the floor and the wood seems pretty damp - Somebody stop this ride I wanna get off!
I am not as concerned about the floor, I think we can handle that part of it. What worries me LOTS is the stringer/transom repair. If it were just the stringer I would probably attempt it with help from you guys on the board. I am concerned about how big a job the transom repair is and how it would affect the structural integrity of the boat. As far as I can tell so far from poking/proding the transom damage is about 2 inch diameter, possibly more but I cant tell yet.
This is an ultra low budget build, but this is my son Bebo's boat who is only 14 now, but I don't want to give him an unsafe boat or one that will give him problems later. Is it worth doing ourselves? If not approx how much would the stringer/transom repair cost. It is a 1/4 stringer boat.
Thanks in advance for your help.
Frank & Bebo