2003 Chevy Trailblazer I need your opinion on buying a vehi

I am buying my mom a vehicle to drive my son around in, and I really like the chevrolet trailblazers. I only have 8000 to spend, so that gets me vehicles with 90-100,000 miles. I have no way of knowing how well a used vehicle was maintained. My question is how many miles can you expect to get out of a trailblazer, if I maintain it from now on? Is it a waste of money to buy a vehicle with 90,000 miles? For $3000 more I can get a vehicle with 70,000 miles, but is it worth that much more money for only 20K less miles? I can't afford a vehicle with less than 70,000 miles. Should I consider another type of SUV? I want one that can get 200K miles on it.