If your looking to get away from the heat, Forget about San Diego...it's to far to really make it a Summer Retreat from the heat. (6 hours one way without traffic).
Try Munds Park (8000 feet) near Flagstaff. 90 miles up the I-17. We leave Friday at 7pm, and opening the first beer at 8:30-8:45PM. Get up Monday morning and leave the cabin at 7am, and your at work by 8:30-8:45am
Vacation Homes work if your with in a 3 hour drive. For Arizona, this means Flagstaff or Payson to Springerville areas. You'll get more bang for the buck, and you won't feel beat after every weekend.
Prices have come down a lot on second homes, and there are good deals.