We hiked it this past October and ended up averaging just under $50/day per person . But we also spent about 6 or 7 nights in hotels and didn't spend much time worrying about our spending. But staying in albergues and eating Pilgrim's Menus (or partial menus like many of the girls did) you're looking at:
5-10 euro/night for dorm room (higher end is only for the nicer private ones)
Around 10 euro for a Pilgrim's Menu (starter/main/dessert/water or wine) or 6 or 7 for just one course.
For lunch we usually spent around 3-5 euro for a bocadillo and Coke.
For breakfast we usually bought some combination of bread, cheese, fruit and pastries the night before and just wolfed that down before we left, around 2 or 3 euro each.
Beer is cheap, but can add up, and then there are things like coffees (which we don't drink but which was VERY popular with many others) and hot chocolates and chocolate bars and anything else that will help you get through the day mentally.
I would recommend hotels at least in towns where you take a rest day (if you take any) so that you can sleep in and really take advantage of the joy of not being in a dorm for at least a short time. We stayed in pretty nice hotels in Leon and Carrion de los Condes for less than $35 euros for a double, singles were even cheaper.
So, all in all, I would say $30/day minimum to $50/day maximum would be a good bet (and I do mean dollars, not euros). Have a great time!