You sure? We have every week shows where you can buy GBB slings from 8 USD, female 2" about 45 USD. Also, it is always meeting point for all breeders, so you can see their webpages and agree on offer in advance and only pick up goods there. Including enclosures. For example, I sent request for glass terra for Pokies, cm 35*35*45 (14x14x18), price is 25 USD, I take it there three days later.Breeding GBBs is a long drawn out, time consuming process...if they were an easy breed, we would see more of them and the price would come down....but when people put in the time they do, its gonna result in higher prices...couple that with a constant and consistent demand as CEC mentioned, and GBB is one T I wouldn't expect to just get cheap.
So, I do not think that breeding GBB would be so hard. But when people are willing to pay so much... Also, where do you buy spiders? Because when I read here about petshops, I am always surprised. No pet shops here sell spiders. If they sell any lizards or snakes, it is always several times more expensive than at show. This is why no one would buy tarantula at petshop, they sell for much higher than they buy. So, do not buy at petshops, but visit shows and buy from breeder directly.