The costings look roughly right. We have a place in the Swiss 4 Valleys and generally drive down unless it's just a long Weekend. We have a SANEF tag as well, and lend it to relatives when they go. Generally, we stop half-way outbound (at le val Moret motel, Magnant, near Troyes) and drive back in one go. You could do it in one go down but if the weather's bad you'll wish you'd taken a break. I'd recommend being strict about swapping drivers every 2 hours, however gung-ho they may be about pressing on. We have winter tyres now and they've proved invaluable on a number of occasions, both en route and just getting out of the accommodation garage. This was us driving over the Jura Mountains this February (on Pirelli Sottozero II winters):
Chains would have been no use here - in alternating thin (like above, at about 800 metres (the highest point was 1000m)) and thick snow you can't be taking them off and on again all the time. We still have them for the odd occasion where it's icy/steep.
Driving means you can take lots of supplies with you and be fairly independent even in the worst case scenario. I haven't used a transfer bus in years since I found myself , wife and three young kids at the mercy of operators who seemed genuinely surprised it was snowing and had nothing on board as contingency for extended delays (food, drink).
