I ve rebuild brake caliper on my current car about 5 months ago. Both pistons are in a very sorry state, so neither the £39 or the £44 service will sort it out. As soon as i get all the parts i will treat the 2 half of the caliper in a solvent bath then a thorough clean then rebuild. For that have been quoted between £135-£175.
That does not make any sense to me. £44 is the price of the parts only you will gonna need for the rebuild.
You can exchange your caliper for £62 at these guys. You send your old caliper they send you back the same model Profesionally refurbished.
No offence but I really doubt DIY refurbishment you may do will be better or cheaper.
But again I understand you I like to mend stuff on my bike too, if you want to do that go ahead and do it