Ryanair
Liverpool to Alghero fly on Mondays only.
Stansted to Alghero, departs 06:15 Saturday 28th £15, returns 10:15 Saturday 4th £90. Flights seem to be every day of the week at the same times and prices (can return on Thursday 2nd for £30).
East Midlands, it's listed as a route but no flights shown so probably not commencing until April/May.
Thomson also fly there but not until May.
Edit: Ryanair prices don't include taxes so add on £43 round trip. Plus £12 each way for one bag, £28 each way for 2! Probably a payment fee too.
Easyjet prices inclusive of taxes, add £7.50 each way per bag, and booking fee of £2 (debit card), £6 (credit card), free with Visa Electron.