Depending on where you are in the UK, I’d drive, but I’m on the south coast. I’ve flown and driven. Time you’ve packed, got to the airport, checking in, flown, baggage reclaim, transferred it takes as long as driving. Parking in Morzine is free in the summer IIRC. Most chalets have some parking.
Driving means you can take lots of spares you may or may not need.
End of June is more ofen very wet and the trails are really horrible with zero grip on the soil. Go end of July or August and it’ll be warm and dusty.
Tolls are about €120 total and its about 550miles in France.
Lifts for a week were €112 in 2019, buy a contactless card that can go in an outer rucksack pocket so you bump your way through the turnstiles.
Don’t try and do the PdS route after the PdS weekend, some of the remote lifts will be shut.
Main centres are Morzine, Let Gets, Chatel, and Les Crosets