Old Subarus burn oil and blow head gaskets, so I would avoid them. The Pilot is reliable from 2006 and newer (silver grille). Anything older has a bad transmission (black grille).
For the RAV4: 2004, 2005, and 2009 and newer models are reliable. 2006 to 2008 burned oil. 2001 to 2003 had a malfunctioning ECM that would kill the transmission.
You won't really find a reliable Mazda SUV in your budget except maybe a 2008 or newer CX-9, and those are just average. The older Mazdas also rust from road salt very easily.
CR-Vs are reliable 2002 and newer. 2007-2011 had climate control problems, though it was only very bad from 2007-2008.
The Toyota Highlander is very reliable. I suggest the V6 models because those are more reliable. every year except 2008 is good.
Every model year Toyota 4Runner can last hundreds of thousands of miles easily. Super reliable. The drawback is that the ride is very bouncy. They do very well in the snow and off road if you get it with 4WD. The V6 models are the most reliable. The 4 cylinders are very slow. This SUV will have the lowest cost of ownership and is cheap to fix. They are expensive because their resale value is so high. Don't shy away from the ones with 150k miles because those could be only halfway through their lives.
The Toyota Venza also had AWD and was reliable.
The Honda Element is practical and reliable, but not available with AWD.
If you have any questions, ask us. Please tell us what your son chooses. Good luck!