I would never tie recording pay to gig pay (I've learned that the hard way - once). The two are separate tasks in my work. If he cannot afford to pay for your work (and $50 per track is way low in my mind), he doesn't get the tracks. Period. When I need tracks from other musicians, I pay them each their going rate. If I can't afford them at the time, I don't ask for tracks.Thoughts?
Seriously, when you tie one to the other and whether or not you get paid in the first place is on shaky ground, it never ends well for you. Bottom line is, value your work and yourself.