With the Bengaii Cardinals, instead of buying a pair, it would be easier for you to fine a male and female seperately and add them to your tank. They should pair up themselves rather quickly and begin breeding. They seem to be one of the easiest fish out there to pair up and breed, but keep the babies to adulthood is the hard part.
The babies require live foods, baby brine shrimp when they first hatch, and then you need to start weaning them onto some of the frozen foods like cyclopeeze and then some of the flake cyclopeeze if you can. You will be lucky if you have about half the fry survive per batch.
As for the cost for a breeding pair of Onyx or Gold Stripe Maroons, you would be looking at around $300 - $500 for each confirmed breeding pair depending on the lineage of them.