HMV are selling buffy Seasons 1-7 for £14.99 each. If you buy all seven, it comes to £95, then get £9.50 back via quidco. I think they do Student discounts too for even more reductions?
If you are not after all seasons, but are needing one or two to complete your collection, this is a great price.
I've put the link to the other seasons on the comments page.
If buying all seven seasons, it comes to £105 (with £10.50 quidco)