Are busses available to take me from Briancon to Sestriere.

I prefer to travel by train. I know the Paris to Turin train stops at
Oulx. I do not live in London this is awkward (5am depature from
Cardiff with 20minutes to get to St Pancras. I can choose the next
Eurostar but that closes the time to get between Gares Nord and Lyon
(on RER D)) so a better alternative for me is the more relaxed
overnight train to Briancon.

Briancon is about the same distance from Sestriere as Val D'Isere is
from Bourg St Maurice. So a bus is possible but it is in another
country so it may not be.

I am certain a chain of busses could exist but that would drive me up
the wall. Briancon-Montgevre, Montgenevre-Claviere,
Claviere-Oulx/Cessana, Oulx/Cessana-Sestriere

If I need to hire a taxi how much would that cost? (two people with
skis).