I'm not sure on the average price but from talking to folks it seems the market on them is a bit iffy since the gene works in a kind of funny way (which is often funnier to explain!). Any banana offspring produced by a male banana will be 100% male. They are often called "male-makers" because of this. Female bananas have a 50/50 chance of producing a male or female. Therefore female bananas are much more expensive than males. The market pricing for them has dropped quite a bit since the male/female thing became known but I'm not sure its stabilized yet. I don't follow BP prices to know what they are anyhow.
Goo luck getting what you want!