$160 dollars an hour.
Do I still have your interest?
Having worked most of my life on commission there is no relationship between how long it takes to make something versus how much the free market will support as to fixed value and more so as to digital content as to who owns the rights once the project is completed.
In context.
Lets say you charge a flat fee commission of $3000 dollars but as part of the contract the client would own the digital content as work for hire they would be free to backdoor the assets as a product for sale in Epic’s marketplace.
The flip side is you could charge the $60-$150 that such an asset would sell for off the rack if you retain the original source rights.
Working on digital IP is not about how much something in front of you is worth but who owns the rights to the digital asset as all copies afterwards is considered as being originals 
As for setting a fixed shop hourly rate don’t do it as the more skilled you become the faster it becomes to complete a project and more so as technology improves and the more your fair use catalogue grows the more you will land up cheating yourself out of what would be consider fair market value.