The length of time it takes to raise any fish for sale depends on the size your lfs wants. Mine likes them larger than some stores and it takes a good 6 months or more to get them to that size.
Price is negotiable and depends on the price your lfs will sell them for. What I like to do is to take the money in store credit instead of cash. It's usually possible to get a higher price that way. Since I spend more there than I make from my fish, it is a good arrangement for both of us.