Pima Air and Space Museum is definitely worth the expense. The last time I was down there they had one of the 787 test aircraft on permanent loan from Boeing that you can get up close and personal with. Pretty neat.
You can get into Pinal Air Park and drive around, but you won't be able to get onto the tarmac, and I wouldn't recommend trying since there's a national guard base at one end of the airport. You can still get a pretty good view from fence.
And as has been said, you can actually see a lot of AMARC from the roads surrounding DM.
Additionally, if you're in the Phoenix area, Goodyear airport out in the west valley has a boneyard as well.