You may doubt that, but in the end, you have no idea what kind of effort something like this actually entails.
Therefore, one makes an estimate beforehand or at least obtains a rough price estimate in writing.
The service has now been rendered, and I don’t see what good it would do to solicit competing offers from the industry.
Especially since it is pretty bad form to seek offers for a service you don’t even intend to commission because you have already received it. People have better things to do than to work from the start for nothing.