Bruk – Can’t comment on the difference between the espace killy and Whistler, as I’ve never been over there.
But, I have been to Val d’Isere for the last 7 years, either at Easter or the last week of the season (end of April). Never been let down by the snow. Tignes is higher, and has arguably better skiing. I prefer to stay in Val and ski over to Tignes. The highest points in Val and Tignes are both glaciers, and have good snow all season. Late in the season, you will get slushy conditions low down – That’s not a bad thing, just different (poor man’s powder, etc).
As for the cost, it really depends on the $ – £ and £ – Euro rates. It may be cheaper next year to go back to Whistler. Who knows? The flight is obviously a lot shorter, and if you fly into Chambery you can ski on the day you arrive, so you get 6 1/2 days in the week if you want them.
If you book ahead, lift pass is around £200, and ski hire around £100 for the week. (I expect a tray would be similar if you need one)
It’s a great area to ski (ok, and to board!). You can cover 50 miles (or more) in a day if you feel like it.