If you want to visit Saguaro NP and don't want to walk, note that the lopp around the east park is closed for renovation.
As for cheap eats, I recommend Las Cazuelitas that someone in the Hilton forum recommended. Cheap-ish eats (quailfies for iDine if it matters). I like the parilla (mixed grill) and recommend the guacamole prepared at your tableside.