Mice? Did you say mice? If there is evidence of them...you've got a huge problem with getting rid of the mess they leave behind. They tend to make themselves at home in the insulation of the floor & walls....getting rid of any "mousey-smell" will be impossible without removing all
the old insulation between the skins & floor, wood, fabrics, foam, etc. To not get rid of it and "just live with it" could pose a health problem...actually getting rid of the mess also could. Yuck!
Oh yeah, welcome to the forums...if you do decide to take on this project (or another), there are lots of folks here to help you along the way.
Sounds to me, unless this trailer is "free" or close to it, you might be paying too much. Check this link
out for some info on what to expect with both the price & repair costs...and what to look at when you go inspect it again.