Why do you charge what you charge for custom orders?
When you have a business that sells music, there are legal issues that make everything more complicated.
To sell recordings of a song, you have to get a license and pay royalties to the songwriters or copyright owners. The cost of getting the license varies depending on how easy or hard it is to get in touch with the publisher. I find myself paying anywhere from a couple of dollars to as much as $20 when I do a song that I have never licensed before. For that reason, the fee for a custom song order (a song that's not already on the website) is $25. That covers the licensing and royalties as well as the production of the recording.
But I want things to be as beneficial as possible for the customers who make the song orders. So if I end up putting their song on the website to sell to the public, I share with them the profits on the first 50 sales of their song. From the first 50 public sales, they'll get 40 cents back from each sale, which means they'll get a maximum of $20 back from the $25 they spent when they made the order. That way, they'll end up getting the music for about the same price as the folks who buy it off the website for 99 cents per part.
A bit complicated, but a win for everybody.