Hi Camel!

Reservation: it depends on what we are planning "après tour". If there is time enough we take the ferry to Corsica in Nice (for which it is necessary to have a reservation if you take it overnight) and an airplane from Sardinia back to Germany. So it is better to have reservations (if you want one special hotel: some months before) for all the touring days. If it's only a round trip there is no reservation necessary, because you are free every day to ride or not to ride.
It is not difficult to get reservations. If there is no free place they will phone for you to check an other free place near by, which means about 0 - 5 km.

JH: (youthhostel, in german it's Jugendherberge, in french Auberge de Jeunesse)
Last year it was about 8 - 14 Euros (in Paris it's about 20 Euros) including breakfeast. Dinner is less than 10 Euros without drinks.

Specially in Germany but also in France they often have small rooms (2 - 4 sleeping places) or rooms for couples or families, but sometimes it's 6 or more. If you ride the col d'Iseran: there are 2 very fine YHs: one in Seez, which is near Bourg-St.-Maurice from where you can start climbing, the other one on the other side of the col d'Iseran (after 80 km) in Lanslebourg. They gave us two diners for the price of one, because they liked us eating so much more than the other guests. The breakfast is ok, too. But there is no great breakfast in France, it's too early for them. The best way is to buy it in a store for the trip and to have a second break in a small cafe.
But there is also a fine hotel (an english couple owns that) in La Thuile (12 km above Seez) whith a sauna and a whirlpool for free (it was nice after a rainy/snowy day coming from col du Petit St Bernard) and with a fat cat named barrel in the pub-like guestroom.

Greetings from Heidelberg
marmotte