Bought 2 of these yesterday in Tesco - should be about £3 per pack. Pack includes 50 plugs and depth gauge measure...
Multi-Size Plasterboard Hollow Wall Fixing
5 fixing sizes secially for different wall thickness
Plasterboard walls vary in thickness because boards come in different gauges and wall coverings, like tiles, also make walls deeper. Multi-Size has the answer, with five sizes in one pack. Plus a depth gauge is included to measure the wall and match a fixing.
You cant go wrong at this price!