I sell my portraits at $30 and up for just the wood piece. If I frame it, I start at $75.
I find that the audience is really important with portraits. People love (and will pay for) different topics. I have had pretty good luck with nature patterns and fishing related things, also pretty good luck with cats. I would have thought that a religious portrait would have been a good target for mexico (sorry for the huge steriotype)
I think your price is ok, you just need to find better people