I live in Sweden , and like you I have a hard time finding supplies at a reasonable price. I use any solid cotton for backing so that is normally not an issue. There's this local store here where it goes for about £2-3. The batting however is really expensive. I buy polybattong on roll which is the only affordable option. I have a quilt top that I am considering getting cotton batting for, but the price is way to high.
If you ever go to London you can get great prices on fabrics ar Whalthamstow market. I've been there twice and did great deals £2 a meter for some small print cotton.
I order a lot from fabric shack, they have good overseas flat rate shipping on up to 9 yards and lots on sale.