If you go to a site like autotrader.com that allows you to look in a certain price range, you'll get an idea of what you can afford. Looking for cars around $3000 - $3500 in my area, 2000 or newer, I'm seeing:
- several cars with well over 150k miles (I'd skip those)
- a 2000 Toyota Camry with 121k miles
- a 2001 Chevy Cavalier with 87k miles
- a couple of 2002-2003 Ford Tauruses with around 120k miles
- a couple of 2002 Ford Windstars with around 150k miles
- a few others
Among those options, I'd be inclined to go for the Taurus or Camry, personally.
I think you'll be better off getting a medium/large sedan rather than an SUV/minivan. You have only two kids, so a sedan is really plenty of space, and you get so much more for your money - not only now, but paying for gas later.
I find MSN autos helpful when researching cars, both for features and so on, as well as reliability and safety ratings.