Check Kelly blue book. For values to set a base, keep in mind that is what some of these or all of these guys are doing is basing their asking price on the private party value from KBB.
And then look at what mileage vs year you are looking for. A 2005 with an average of 10,000 miles per year that would be at about 70,000 miles right now. But I drive about 20,000 miles a year, so my car would have 140,000 miles if I had owned it since day one.
And the repair issue, I don't know their specific situation, but it sounds like they need the money. That doesnt mean its a good deal, you are looking at the car, overall whatever deal finally works out for you should be a car that you feel confident was worth the money you spend.
But I would look at a few high mileage ones. I know that subaru makes great cars, and a lot of us love our cars. Your best deal may be with higher mileage on a well taken care of vehicle rather than a low mileage one that some one can not afford to repair.