A family annual membership to the UK National Trust costs £104, but join the Scottish National Trust and the price is just £69.40 for a year. Membership of the Scottish National Trust also allows entry to over 300 NT properties in England and Wales. Parking is not included outside of Scotland, but as an English NT member I've never been asked for proof of membership to get free parking in their properties (I know there are some where parking charges are enforced though).
Membership prices for Comparison (English / Scottish - paid annually by direct debit. Prices reflect 25% discount in first year):
Family (2 Adults + children): £104 / £69.40
One adult family (1 Adult + Children): n/a / £45.75
Individual (1 Adult 16-25): £30 / £16.90
Individual (1 Adult 26-59): £60 / £39.75
Individual (1 Adult 60+): £60 / £39.75
Following the first year's membership, all prices will be +25% (English NT included)