I would say that bus is closer to full size than mid-size. So it's a 1994 International with 7.3 engine, eh? I would infer then that it has the same engine as my Ford F250 pickup. Indirect mechanical injection with rotary injection pump. Some people really like these engines. I've had problems with the injection pump, but then I was messing around with home-made biodiesel and that may have been a factor. Personally, I think I would prefer the 6.5 Powerstroke with electronic injection, but I would not say the 7.3 is a bad engine. If the injection pump goes bad it will cost you about $1,000-$1,500 to replace (ask me how I know
So you currently have 3" headroom in there - depending on how much you insulate your floor and/or ceiling, your headroom will be reduced by a certain amount. I'd say you will likely lose 2", leaving you just 1" from the ceiling. I am 1/2" from my ceiling, and I can tell you I'd rather have a couple inches above my head. I don't think I could comfortably full-time in my bus - I'd have to raise the roof.
Regarding price, well... price varies depending on who you buy from. Looks like you are at a bus dealer, right? In that case, you are at the high end of the price scale and I would expect to pay about $3,000 - $4,000 for it. I wouldn't go above $4,000 unless I was truly desperate and had very few other options. What are they asking for it? I don't think Motobus' suggestion of $1,500 is going to fly at a dealer, but then I'm not a very good negotiator. I would probably start at $2,500 and hope to close at $3,000. But I'm guessing they are asking like $4,500 for it.