Wife and i hiked the Camino about 5 or 6 years ago, during the month of July. We didn't start in St. Jean, but a little further from the France border but still in the Pyrenees. Don't remember the name off the top of my head.
When you sign up as a Perigrino (spelling?) aka pilgrim, it entitles you to "deals" at the various different hostels/places to stay and even often restaurants. It's relatively cheap at most of these. I remember it ranging from about 4 euro to around 15 at most. Some places to sleep at are donativo, run on a donation basis. A number are connected to churches.
The actual hike is fairly easy, though i heard from some others that a number of people got some injuries right away when they started from St Jean because it's got some pretty steep downhill and your not yet in the rhythm, muscles etc, aren't warmed up, and some people go too fast at first.
Lot's of people i met had blisters at some point. I had a different system down than most, and didn't get a single blister.
Met plenty of people in their 50's, 60's, and occasionally even older, and plenty of them did in it the around 30 days which is average for most who are not more hard core hikers, young bucks, and the like. Most people seem to range from about 25 to 35 days (that we met and talked to).
Camping is very frowned on, and one person told me it was illegal. I had brought camping stuff, and we did camp a few times until we were told about that. When you're sleeping at the Hostels, definitely bring something like a silk sleep sack, or otherwise tightly woven, but light full covering to avoid issues like Donna mentioned.
Brush up on your Spanish before hand if you need it. One of my misconceptions was that a lot of Spaniards know English pretty well... well maybe in the cities, but not so much in the country. Course, there are various languages besides Spanish, and while some who don't normally speak it (like the Basque), well they do know it.
Best advice i could give, is go into with little preconception and just be open. Surrender, that beautiful Feminine word that is so foreign and difficult for most men.. The Spirit of the Camino was amazing, for me it was the best part, the sharing of meals, of stories, of friendship, openeness, kindness and helpfulness.
I'm more a relationship kind of person and more internally focused than many, and so i forget a lot of the names, places, and details of the outer stuff, but the connections and relationships are still fresh in my mind. I now have friends all over the world. The reason why we went to Quebec City, was to visit a couple of Camino friends (two different people not connected to each other).
I couldn't recommend it more, unless you're looking for a more purely nature, natural hike. There is plenty of nature, but there are points wherein you're walking through or around cities, which for me wasn't so nice especially after being in the more natural places. Getting to Galacia...wow amazing, very different feel, look, and even the people tend to look different--much more Celtic like and the land is much greener--almost reminiscent of Ireland in some ways.
If you would like more and better details, i can put you in touch with Becky (wife), she is much better at the places, names, and details kind of stuff than i (she is A LOT more outer focused than myself), and she has been to Spain 3 or 4 times now (but only once did the Camino).