If you get alot of them framed, it is worth trying to find a local framer who may consider a discount. I just took 3 large ones in, average 30 x 30 cm and it cost me $280 to get framed..for all three. When i pick them up i shall post them in my SAL thread, any day now..

I get a 20% discount.
that = about 160 pounds so just over 55 pounds each...but obviously everyone has a budget so for some this may be expensive. I also work an extra shift to pay for them as I am not flush with cash, unfortunately
Another trick is to get framed pictures that are fairly cheap, like at those shops(I am asuming you have them in UK) that sell dirt cheap stuff. Take the picture out and use the frame and glass...or try a junk shop for a cheap picture with a nice frame. Recycle is good and cheap.
Photo frames is another thing I use for smaller works, I use double sided tape with those, it''s impossible to lace with a photo frame cuase you end up having to go over the back of the frame backing board and it doesn''t sit flush..well thats what i found anyway, plus it looks yukky at the back.