Why?
No-one should be paying anything before someone actually comes out. Most people give free quotes. Except maybe someone who is coming to do something in an emergency that needs doing now. Like fixing boiler/heating, or plumbing. But even then they wouldn't charge until they've done it.
£180 for what the OP had done is fine. There would not only be the parts, but also his skills and qualifications, and also the time doing it, and the time spent travelling to and from the OP's house.
I was speaking to people about this yesterday - and this morning, and have asked 3 people what they would expect to pay for this job - including VAT and labour and parts, and testing and re-testing the system, AND the travel time etc... The 3 answers were £170, £220, and £250.
Then I actually googled how much it should cost, and got this...
The average thermostat installation cost is £275, including labour and materials. While it sounds affordable, the overall thermostat replacement cost can balloon to over £300 due to many factors. This guide will help you set your budget..... 14 Mar 2023.
So actually, @Gettingbysomehow you got a good price actually!