Generally the best place to find cheap skiing holidays in France is through the internet, as there are a number of websites which specialize in exactly that.
One of the best is snowtrex.co.uk, a site which offers both budget and premium holidays, however its cheap offers are among the best out there, and while France is rarely the cheapest place to go skiing, snowtrex currently has some incredible deals, for example 7 nights in St. Sorlin from £163 per person. The site is also easy to navigate, with many of its best deals highlighted on the home page so you don't have to go digging around for them.
If you're fairly flexible with when you want to go or are able to book at short notice, then last minute is also a great site to get cheap deals. Although it is a general holiday site rather than specialising in ski holidays it still has a lot on there and also provides useful extras such as car hire offers.
If you're after a package holiday then crystalski.co.uk have some very competitive offers and best of all they take all the stress out of the experience by offering airport transfers, supplying your lift pass and having resort reps to help you out over the course of the holiday. They also organise optional excursions and activities above and beyond the skiing.
Whatever you're looking for in a cheap ski holiday one of the above sites should be able to provide it for you and before you know it you'll be cruising down the slopes, looking out across the Alps.