What each one asks of you
Timber is painted or stained, and that finish is the maintenance. In a wet Highland year the paint is what keeps the frame. Miss it for long enough and the timber moves and the joints open. The advantage is that a joiner can match a slim section and a colour to an older front, and a damaged part can sometimes be repaired rather than replaced as a whole unit.
UPVC does not take that paint cycle. The colour is in the frame, or in a foil, and the maintenance is washing and checking the seals and the hinges. It is a poor choice when the section is too bulky for a stone opening that depends on a fine sightline. It is a straightforward choice when the house already uses it and the new window only has to match its neighbours.
This page does not list a price for either material. A surveyor confirms what the property needs.
Which streets in Inverness
Older stone streets by the Ness, the Crown, the Haugh and the centre are where timber, or a UPVC section that keeps the proportion, has to be judged against the stone. The article onreplacing windows in an Inverness stone house stays with that front.
Later houses at Inshes, Slackbuie and Culloden, and many post-war houses, are where UPVC is already the ordinary frame. Matching the existing colour and the way the window sits over the sill matters more than a debate about tradition. Westhill and the eastern estates are the same kind of question.
The service page, if UPVC is the frame you want looked at, isUPVC windows. This article stops at the comparison. It does not specify a system, a U-value, or a warrant.