I know that the purpose of primer is to make the walls ready for paint. I know that it seals the drywall and joint compound so that paint won't be absorbed unevenly. That's the limit for my understanding of primer.

We have drywall going up in my husband's workshop, so it will be a new previously unpainted surface. I have a reject color of paint that I'd love to use up as a primer coat if I can. Is that feasible? My reject can is BM Regal flat (if that matters). I'd plan to paint 2 finish coats of my final color over top of that first coat. Or do I just need to suck it up and buy yet another $50 gallon of primer?

Thanks!