Seems to depend on sizes. Not all stockists cover the full range and those that do often, and understandably, charge a little more. If there is a Jessops near you, I'd explore their order on line and delivery to the nearest branch. It's quick and there's no postage charge. Secondhand Darkroom Supplies on the other hand have to charge unless your are close enough to Witney in Oxfordshire to collect but their actual prices excluding postage probably puts them close to Jessops.If it is a close run thing then SDS deserve support as they cover all manner of items and we need such stockists to stay in business. They are especially competitve in Warmtone paper at 5x7 and 8x10 and postcard paper. Can't say about 12x16
We've had a few harsh words to say about Jessops recently and justifiably so but my very recent experience of its order on line and delivery to its Northampton branch has been very positive.
I'd trawl the sites to see what you come up with in 12x16. I know of the the two mentioned above plus Nova, RK Photographic, Silverprint, Keyphoto, Firstcall and MORCO.
You may see 100 +20 sheets in 8x10 Ilford MG IV Deluxe in either finish come up as brand new on e-bay. It most likely will be just that. Jessops it appears have been selling off the student packs for £9.97 per box. I 'd be surprised if a few enterprising souls or is it profiteers haven't bought a stock just to re-sell on e-bay.
pentaxuser