Breeding age males look to be in the neighborhood of $200 or less, generally speaking. Females are quite a bit more; only one I could find that was breeding age/weight and proven, the asking price was $1,500...for a single-gene yellowbelly female. Another one is listed on a different classifieds site for $650 for a 1,000 gram female (doesn't list her age/date of birth). That ad is from April 4, so who knows if it's still good or not.

Did a search on that same web-site and found an ivory female for $800, shipped. Are you wanting to produce ivories to sell or have one for yourself? You could always get a younger female, raise her up for a few years and then pick up a male later on. Males take no time to get to breeding size and if you don't mind waiting a little while, you could probably find a 2010 or early 2011 yellowbelly female for not too much.