Nest can quite easily be self installed. Took me 30 minutes including removing my old stat.
NestE - £150
Nest Gen3 - £180
Tado - V3 Starter Kit £178
Tado - V2 (discontinued) Starter Kit £100
I do not see that being a lot cheaper unless you are happy to buy the discontinued model
I was under the impression Nest needed a different Amp on the wiring and some features were restricted to a monthly subscription? It's been two years since I looked at it though.