Here is what I have learned during forty years’ of commercial work:
Finding work is not difficult. Getting paid for your work is often impossible. Remember that you are doing custom work which has no resale market except to that one client.
Every job comes with a preset budget. You must first determine the budget and then adjust your photographic quality to fit that budget. If the client insists he has no budget, stop right there. He probably has no money. Lots of people order expensive photography with absolutely no idea of how they will pay for it.
Submitting a bill after custom work (which is of no value to anyone besides the client) has been completed for an amount exceeding the client’s expectations will result in non-payment. You might get your exposed film back (after a legal fight), but you won’t get paid.
What’s worse, you will lose the money you spent for processing, materials and other expenses. I repeat: determine the client’s budget before accepting the assignment.
Second point: wherever you are, there is a market rate which has been established for various kinds of photography. That rate has everything to do with usage, competition, etc. It has little to do with your cost in time, materials and expenses to produce the work.
For example, in the days when commercial photographers shot film, they charged approximately double their hourly cost of doing business to shoot in the studio. Then the time spent developing and printing in their lab was given away for free. People were willing to pay big money for photography, but not for film development.
It is just as bad to charge too little for your work. I call it the “Jewellery Store Syndrome”. No prospective bridegroom would purchase a diamond engagement ring for one dollar (or one pound). Even if the quality were perfect. His bride is “worth” his paying considerably more.
If you quote a price dramatically below the market price in your area, the client will think he is commissioning junk work.
In summary, find out the market rate for the job in your area and make sure the client is willing to pay that rate before accepting the assignment. Adjust your work so that you can make a fair profit at that fee.