Both the original trilogy and new (i.e. episodes 4-6 and 1-3) are available in box sets instore for £12 each.
Original trilogy showing as £15.43 from Asda online.
Purchased both titles today from their Rainham store.
Might be able to purchase through their online groceries site to get a massive 1% Quidco?! Although I suspect that's strictly groceries only.