Maybe not cheap, but rooftop yoga classes mean exercise and a view. How cool is that? And Sutra yoga is offering free yoga in various Phoenix parks on Sundays. Plus, on their twitter stream they sometimes offer "$2 Holla" classes where a certain password gets you in for $2.
April 12th is "Mai Tai Mania" at Trader Vic's, where $15 gets you drinks and niblets. "Trader Vic" Bergeron invented the Mai Tai, folks. And they are good. I know from personal experience.
My mom and I saw "The Philadelphia Story" at the Biltmore Fashion Center last night (whatever it's called--up at 24th St and Camelback). They are showing movies on Fridays at 7:30pm for free. Bring your blankets and chairs, take a picnic (if you buy something they validate 2 hours of parking), but leave your fear of wolves at home. I swear, I turned around the corner and saw this big tan colored dog and thought, "Wow, what is that--it's as big as Billie, and so gentle with those kids," and holy hell, it was an actual wolf or wolf mix of some sort. Really and truly.
Oh, and the Origins up there is giving free mini facials or samples to sell people on face cream. I like to score free stuff, but the timing was just not right for me to take advantage.