How to fire a client and justify my worth at the same time!

So I am a freelancer and have a client who asked me to design them a bot to integrate into their website. They told me their initial budget which was in line with the costs. I quoted them and they agreed and we got the ball rolling. It quickly shifted to then wanting me to duplicate what I had done to on-sell to their clients. When I said okay it will be $X and you will also have to factor in ongoing training and maintenance, hosting, LLM costs etc.

At first it seemed like a good idea because there were people lined up around the block and it would basically mean I can duplicate them and keep them running etc.

Well now there isn’t a huge amount of clients because the build costs are too high and the running costs are too high, they can’t sell them. They honestly act like my boss and tell me they need this by tomorrow as they have a meeting and need a demo, they insist on me (and my engineer) working at lower rates and is not adding our margins on to LLMs etc etc.

I then discovered they’d set up a business selling what we do and therefore acting like we’re employees. We’re business owners who have other (sane clients).

They have now said they built one online and used that because our (customer built one) wasn’t ready and saying “this one is only $29 a month I need a details description of why yours are more expensive.”

I know everyone is going to say just tell them to eff off but it doesn’t feel that easy.

Any suggestions on how to word a good email? I have drafted 200 but not never don’t this before and am a bit to emotionally stressed and confused about how to explain why we are more expensive and I want to end with that explanation but I can’t think!.

Example - if a client suddenly just built a website in Wix after they’d started a customer project with you or your agency - what would you say to justify your prices?