First they don't sell enlarged photographs these are litho prints so the economy is in the scale. Many are produced in China & the far east and the unit cost is very low.
I can buy a really nice 24" square wooden frame in the Range (not sure how far North they've expanded) for £7 that has to be coming into the UK below £3.50 less if coming through a third party importer. They buy the images for the prints from picture libraries the royalties are quite low per print.
Stoo Batchelor and I ent to a St Ives gallery selling photo's in April, mainly shot by the owner, who works full time elsewhere. He has staff running the shop/gallery and a wide frame inject printer churning out B&W and Colour prints most of the day and he also sells litho printed cards. He has a few genuine silver prints of Bill Spears work as well.
That approach seems to be quite successful for him but the area is very geared to Tourism and the images (apart from Bill's) reflect a romanticism of the area.
The same could be done in Derbyshire with images of the Peak District. You'd need a town that nearly every one visits. St Ives works well because nearly everyone visiting south Cornwall goes there at least once while there.