So I made to Andorra and it has been great.
I got in contact with a local agent, that arranged me a studio for 1 month for 1200 eur in Pas de La Casa. It is in a walkable distance from the lifts. (less than 100 meters)
Internet at the studio is not reliable, but I arranged to use the agent’s office (that has 280mb fiber) to work.
Grandvalira is a huge resort. 210km of runs. I’ve been for a couple weeks and still finding new spots. Snow in the last days was amazing, and during the week the mountain is not busy.
No need for a car at all. You can get here from Barcelona or Toulouse by bus.
Andorra Telecom offers an ok 3g service here. 10EUR for 1GB prepaid.
local travel agent: http://www.snowevo.com
after all, besides the internet that can be tricky, everything was pretty easy and affordable. Grandvalira is not a fancy resort that is really fun. I think will come back for a longer stay.