Yes, I agree that's a fair price, CW. He's obviously not making a drama out of it as some do.
Assuming it's no more than the usual two storeys high, scaffolding is not a lot of use for ridge tiles. Maybe a good quality tower scaffold at a gable end. With ridge tiles, once you're up there, it's safe enough. Not my favourite job, though. Scrabbling along the ridge with tools and a bucket of mortar.
It all depends on the access; shape of the building; roof height etc etc.
I can't say much about the flashings without seeing them, but, usually, if they cover your roof, then they are yours to deal with. It all depends on who has the benefit of them.
For the roofspace/loft .............. it can be of interest to see if there's any new or historic damage. But, the only sure way of checking the state of the roof covering/flashings/valleys etc, is from above. For instance, in older roofs with no sarking felt (under the slates/tiles, it's quite common to chinks of light. It doesn't necessarily indicate a problem. Roofs aren't "sealed", they are merely "lapped".
If it is felted, then you won't be able to see anything at fault with the covering anyway.
///"Roofer has also said this may not solve the problem"/// ................