This doesn't seem a bad deal at all for a ski holiday 16-23 December, especially as for some it's the school holidays. This price is based on a family of 5, 2 adults and 3 children however it's only £40 more in total for 5 adults.
Book a package for the accommodation which includes ski hire and lift pass on snowtrex.net Price for accommodation, lift pass and ski hire for 5 people (can be adults or children, same price) £695
Add on linen and towels for €10pp and a cleaning set which I presume most will need for €7 (you pay on arrival for these extras) €57/£50.08
Book flights from Luton to Grenoble, total for 2 adults and 3 kids is £292.95 or for five adults is £332 book on easyjet.com
Book car hire on vehiclerent.com £155.91. The car is suitable for 5 people, so is fine for 2 adults and 3 kids, however may be a bit of a squish for 5 adults, but the resort is less than an hour away from the airport so it is only a short journey.
Total price, basing on a family of 2 adults and 3 children is £1143.96/£228.77pp. It's around £40 more in total for 5 adults. If you have 6 people it is likely to be even cheaper.