It's all really just a matter of perspective. If someone wanted a basically stock trailer and their plan was to restore this one... That's an awfully tall order and possibly not worth it. Although - a similar trailer in decent (not stellar) condition would be worth a MINIMUM of about $3500-$4000, so the buyer would be able to spend up to $2000 - $2500 before it really started to fail to show a good return.
Of course - if their plan is to gut and redesign, might as well buy one where the stuff you're gonna rip out is already burned out. Let's you buy the shell as cheaply as possible. In that case - the cost of your refit is going to swamp the cost of the raw trailer anyway. Overspending a bit at the beginning isn't that big of a deal if it means finding a trailer you can work with. Especially if that trailer is close to home. The price of gas to pick it up can't just be dismissed as a non-cost. I'm willing to pay more for something if it's closer to home.
Replacing the fittings (vent/fan/etc ie all plastic trimmed items) isn't really all that pricey. It's a lot cheaper than a professional paint
job, and many on the board have been willing to spring for that.
Seemed to me the biggest pain in the rear on this one would be replacing all the wall coverings. I suppose the existing material might be salvageable. There ARE companies who specialize in fire cleanup who could likely do it. The glass is LIKELY OK with just smoke damage. It'll stand up to some VERY harsh cleaning approaches and worst-case can be painted to seal.
I'd definitely be worried about getting the smoke smell out of the thing though.