You didn't mention anything about HVAC - does it have one currently or does that need to be replaced too? If you need new central ac/heat system that will add $4-5K more. If you go with all window units they will need heat too for IN winters, so probably $500 (x 3 or 4 units) = $1500-2000.
If it's a 90's model it likely has a gable roof. I'd strongly consider a roof over with a 26 gauge metal roof. I'd sub it out so it's done right (unless you know how already). Make sure the roof overhangs the eves by 10-12" so water runs off onto the ground and not down the side of the home. It should run you about $2500-3500 if you sub it (materials included). That will be a huge selling point for your potential buyers.
Whatever you sub out, you should provide materials and pay for labor only. I have spent a lot of money letting contractors supply materials only to find out they mark them up 20+% because they went and got them - you should do that yourself - there's a lot of education to be had in procuring materials.
Lots of good content on youtube about MH remodeling - check out Drews Mobile Home Repair channel. Has some great roofing and floor repair videos.
Best of luck!!