IMO the best bang for your buck is to take an all inclusive guided holiday. September is the end of the summer season in a lot of places for the lift system is shutting down (or did so at end of August), as such the van uplifts of the guiding companies are very useful as well as the fact that they know the best trails. Weeks at that time of year are generally branded “back country” and are a mix of pedalling and van uplift. The one exception might be Chamonix which for “epicness” is hard to beat, there is a good trail guide book available (look on Zero-G’s website).
Holiday company suggestions – Trail Addiction, White Room Chalet