Tub Stains

I have a really really old tub, like we’re talking thirty-forty years old.

Anyway, it’s white, or used to be.  And I’ve tried magic erasers, and I’ve tried bleach.  I’m just at the end of my rope.  It’s such an eye-sore that I’m debating re-doing my entire bathroom, because I honestly am embarrassed by the stains and the terribleness of it.  It’s a ring and then some spots.  Anyway, what I’d like to know are options that I have instead of spending a few grand in redoing this damn thing.  Is there such a thing as a paint, or…. like a cover that I could use?  Or any further spot treatments you all have tried that work?  
Thank you all so much in advance!