If the flash sales are anything like last year, it will likely be the more expensive sets. It was mentioned specifically that the flash sales would be geared toward higher end products. Last year we had Cardcaptors CE, Neon Genesis LE, and I think there was some ultimate edition sets in there too. I think everything was £50+, so postage won't be an issue in those cases.
I'm quite looking forward to the flash sales and seeing what some of the long out of print stuff is. I think the flash sales are likely to be the best of the lot in terms of price, since last Christmas I haven't seen Neon Genesis LE, for example, available anywhere for the £59.99 that it was for those few hours last year at ATA.