The S90 is a very nice car. But it is old, there is a lot of work to get one up to dependable condition. The MPG is dismal, not bad for its year, but that was a long time ago.

I suggest you open up your options a little to a more modern vehicle. The normally aspirated S80 has the same bhp and is still quite luxurious. Example:
http://chicago.craigslist.org/chc/cto/4226733930.html

I would avoid any Volvo built in 2001.

Of course, if there is no detailed maintenance history, no deal!

And if the cabin blower makes any noise in an S90, forget it.

You didn't mention if you performed your own repairs, this could be a deal breaker as garages see dollar signs when a Volvo arrives.