Excuse me, but a 17tyh edition board with capacity for 10 circuits, with 2 x RCD's and 10 MCB's would be £100+
Then there's earth upgrading 16mm tail to earth point, 10mm bonding of gas and water, 25mm tails for live neutral feeds.
Add pre and post testing- 5 hours
Add actual work- 4 hours for simple board change over
Add extra time for line 2 of post
Then there's the paperwork, registration with a scheme provider, test equipment, tooling, van / wheels, training cost pay back and pay back for years of college.
Consider safety and working inside regulations as more important than 'simple' cost. £500 could be a reasonable figure and that figure could mover up or down subject to survey.
No doubt you have a pile of electric devices worth far more than the cost you suggest is 'unreasonable' and yet the very heart of your electric system is the most important part.
Cutting cost is a very false economy and I'd suggest you wise up to the fact that going down the cheapest route is a very unwise move.