$300 is not bad for if it's a female. You have to expect to pay a little extra from a pet store, but if it's a great looking female that is not a bad price at all IMO. Is this a store that specializes in reptiles? Seems kind of odd that no one there could sex a snake for you. Just a suggestion, but if you are going to really get into buying morphs and expanding your collection you should really learn to sex your snakes. I double check every snake I buy no matter who they come from and I have actually had a mis-sexed snake arrive on a couple occasions. Nothing could be worse than spending 2 years raising up a snake that you were sold as a female only to dicover at breeding time that it is a male. I have read about it happening many times.