Purely on a supply and demand basis you have to believe that when the demand for goods and services takes a big jump, as it will in 2010, and the supply is relatively fixed, as it is on most of the caminos, that the prices will go up.
2002 CF: 2004 from Paris: 2006 VF: 2007 CF: 2009 Aragones, Ingles, Finisterre: 2011 X 2 on CF: 2013 'Caracoles': 2014 CF and Ingles 'Caracoles":2015 Logrono-Burgos (Hospitalero San Anton): 2016 La Douay to Aosta/San Gimignano to Rome:
I walked in the last Holy Year - 2004 - and was amazed to find that nothing much had gone up since I'd walked in 2002. And, things still hadn't really changed last year.
The albergues still charge 3 - 9 euro: the menu del peregrinos are still under 10 euro. If you buy stuff from Supermecados, the prices will be the same for locals, tourists and pilgrims so I can't see how one Saint's Jubilee year can affect prices that much. Perhaps in Santiago itself prices might increase around July.
Another thought on top of what has already been said: there will certainly be more people in 2010 and therefore it is possible that you will have a harder time finding space in alberges. If this were to happen you may need to take hotels (or pensions or casa rurals) - which would be more expensive of course and you wouldn't be able to cook your own meals as you can in some albergues. That would double or triple the cost of your trip if it were to happen frequently.
In 2007, 27,140 pilgrims arrived in Santiago in August, and 8,112 arrived in April. If adjustment is made for the time it takes to walk the Camino Frances, if you start in March you will compete for a bed with about 1/3 the number of pilgrims as you would when starting in July. You NEVER will be concerned with the "bed race." There is plenty of bed space for April starts, too. Problems can begin in late May.
About 80% of the pilgrims arrive using the French way. No one reports the number of pilgrims who walk, but do not get a Compostela. About 1/4 of those receiving a Compostela for the Camino Frances have walked only about 100 km.
The numbers will be off-scale in 2010 (Jubilee year 2005 had 180,000 Compostela-receiving pilgrims compared to 75,000 in 2004 and 115,000 in 2007), but the real crowding will be in the last 100 km during the week before St. James birthday. I doubt that anyone will be surprised if 250,000 Compostela are issued in 2010. Santiago will be mobbed all during July.
The statistical conclusion (please, I am not TELLING you what to do!!!) is to avoid the Camino in 2010 unless you walk very early in the year, or in the autumn. In other years, crowding begins in June, mostly toward the end, so start mid-May at the latest. March and September are excellent starting months to avoid crowds, but some albergues do not open until April.