I cant offer much advice re booking cheap holidays except for possibly trying to avoid the larger resorts and book accommodation in some of the smaller satelite resorts which share the same ski area (as long as they have their own beginners area and ski school), but some tips for being first time skiers going on your first trip would be:
1) Deffinately invest in a few lessons in a snowdome before you head out to the alps. If you are spending a substantial amount of money on a holiday you want to go and get the most out of your time there so a couple of lessons before you go will make the first few days much more enjoyable.
2) They will be shattered if theyve never been before. Spending a whole day in a snow plow will shatter out kids and the mrs alike so it might be worth trying to find something non self catering as everyone might be abit too tired to cook and clean etc.
3) Get the kids started early. If they do want to learn to ski at all (and why wouldnt they – its awesome) then the younger they do the more they get out of it, its much harder to try and learn when youre older.
Just a couple of my thoughts.