Cheapest way is to get a holiday provider to buy it for you, thus you get to cash in on their bulk purchase.
Alternatively, buy an area pass for 6 days. This offers unlimited uplifts across the whole of the PdS region. You can also buy on a daily basis or as I found out last year, you can get a certain number of uplifts, useable on any of the lifts in e.g. Les Gets. Thus, for a variety of reasons, I now have a spare ten uplifts that i will use when I am next there.
Also- try to get hold of a winter pass- you may well get a discount on the summer prices. It is always worth buying the electronic pass, the convenience at the gates as you juggle your bike through is well worth the few uero’s it costs. I’ll happily send you one if you promise to return it asap after use, I have a few spare.