There are dozens of retailers online. Everything from Wet Spot to Pet Zone. Check them all out.
Shipping (express/overnight, generally) is always going to be roughly $30-$50 for fish - depending upon your location and the source.
But if you can find a hobbyist with them? Those prices will likely be lowest and the fish healthiest. So search the For Sale section to see if anyone has sold them in the past. And then post a Want To Buy thread in the RAOK/WTB section with the specific fish you're looking for.
Note: Moved this thread to a more appropriate area of the forum for you.