Cost is not everything. I had intended to renew my dads consumer unit for years, but while having the outside loo and pantry made into a wet room the electrician offered to swap whole consumer unit for £100 extra, saved him fitting a henley block and mini consumer unit for wet room. At that price I jumped at it, without considering the skill of the guy doing the job.
When I arrived at the house the poor guy was pulling out his hair, he had no meters that I could see and there was an earth leakage fault he could not find, he swapped one RCD for an isolator and promised to return next day, he was never seen again, and the builders who had employed him seemed to be trying to do remaining electrics themselves, I suspect now the builders had cash flow problems so to be fair the electrician may not have returned because he found he was not being paid.
For me the electrics was the least of my problems, that I could sort, but had the same happened to a family where nearly every male was not an electrician of some type, it would have been very different. Don't go by cost, go by recommendation, find an electrician you can trust. I did not learn, for a second time I was temped by cheap electricians when I wanted the job done fasted than I could do on my own, needed to be done before my mother came home.
Let the electrician doing the work advise, what seems a major job may be simple and the reverse. The big one is deciding if two RCD's is good enough, all RCBO's is more expensive but less likely to cause problems latter, but there is also the mixture. On this it is up to you, but some one on site can advice far better than some one on the internet.
