We too had some extensive water damage which we found after the purchase of our camper. It was disheartening but we dove in without any prior camper renovation experience. We did it one step at a time, did some research here and YouTube when we needed some knowledge and after two months of continuous work we are almost done. Our floor corner looked very similar to your wall picture. It can be done, it will just take some time and effort and yes, some more money. Ours did not cost anything near $3,000. Not even close. In our back wall and partial side walls we replaced some wall studs, floor joists, subfloor plywood, replaced a lot of insulation, replaced a wall and redid the flooring through almost there entire camper. It will be much cheaper if you can do the repairs yourself. I would guess we spent about $1,000 for our supplies and I didn't even list everything we purchased.
If you decide to tackle this project, here is a link to our journey http://www.rvforum.net/SMF_forum/index.php/topic,103798.0.html
If you have questions the forum members are really good about chiming in to give you any advice they have to share. After finding our damage we were upset, angry, hurt, frustrated. Once we accepted our issue we became determined to make it the camper we desired it to be and expected it to be from the beginning. Good luck and maybe you will finally have the camper you dreamed of from the beginning and you will be able to have some adventures to share with everyone here and stay a part of the rv community. You have support here.
.
