How old were they when they were first aquired? What are the lighting conditions? If they don't have some sort of photoperiod then they may not breed. What temperature are they being kept at? If they are too warm (or too cold) then breeding activity will be affected. Mine are breeding fine at 55/65 degrees, though high 60's to low 70's are probably best. They tolerate cooler temps much better than warmer temps. It could also be possible that either your male or female is a "dud". You could try adding more females, and if that still does not yeild any results, then I would suggest trying to replace the male.
Also, just noticed that you only mentioned feeding the two BCI. If you are breeding rats with the intent on conserving funds, you are more likely spending more breeding them than you would be by buying them. It is rarely economical to breed feeder rodents for only a few animals. However, breeding rats can be fun, and it is very convenient. Also, you can't beat quality control
Anyhoo, good luck with your breeding, hope you found something useful in there