Epoxy Primers... Is there a difference?

[Mrfixit]

I need to buy some epoxy primer for my project but the price range is HUGE! Sherman-Williams $150 Gal, House of Kolor $114, Eastwood $89, etc. I need to spray it over some bare metal (steel) before I do bodywork. I don't mind spending a little more if the product is better or has more advantages but from what I've read, they all seem the pretty simular. I would like some opinions and recommendations for a epoxy primer that is considered a good value.

I look forward to reading your recommendations.