I lived in Kendal for 30 years, and although it's not in a National Park it is close to The Lake District & The Yorkshire Dales
They are both attractive places to live, which is reflected in house prices, but there are a couple of other considerations. Both planning boards are very strict in applying the rules - some would say petty. And the traffic can be very busy at times
The red tape in the Lake District could well get worse as it has recently gained World Heritage status
No doubt these factors will apply to other Parks as well
So the trick is to live close by on the fringes of a Park, but not actually in it. This has become a bit more difficult for The Yorkshire Dales & Lake District as they have recently expanded & merged
NE Cheshire, to the SE of Stockport, say around Marple or New Mills will give you access to the Peak District and the shopping & fleshpots of Manchester
The area around and just north of Nottingham & Derby is quite pleasant & rural & reasonably priced if you find the right spot, but will give access to the Peak District & the M1
NE Lancashire and the South Pennines, Ribble Valley, Forest of Bowland, & Pendle are rural and attractive, and you can get to Manchester, M6, M 65, M62 and so on.
The old mill towns like Burnley, Colne, Blackburn and so on are cheap but scruffy, though like anywhere there are good parts, with some nice villages nearby
Shop around for house prices, they are in direct proportion to the distance from these towns towards the countryside; there are smaller towns that are a bit more desirable, like Skipton & Clitheroe.