If you have either a smart phone or a device with Wi-Fi connectivity, you can use
www.booking.com to locate small hostals, private alburgeues and hotels perhaps a couple of days in advance, once you know your pace, capabilities and the weather "down the road." On my two
Camino Frances (C/F) trips (2013, 2014) I used my iPod Touch with the free Wi-Fi found frequently along the C/F. It worked perfectly.
Also, you can also use the Google Translate app to create and save on your device a thread of reusable phrases, e-mail requests, or replies that you can update and change on demand. Thus, even speaking only basic "Camino Spanish" and not being able to phone direct myself, I was able to send an e-mail to request an advance reservation, and reply to what the location sent back to me. Consider though that they may only check their "in box" once daily. So plan accordingly. You can also use this technique to navigate pharmacies, taxis, buses, supermercados, centros de salud (health centers) etc.
Also, make sure to notify someplace you have a reservation by e-mail if your plans have changed and you no longer need the reservation. This is good Camino etiquette and will help another pilgrim. Good manners and consideration are always appreciated.
I found that some private albergues had web pages, or at least e-mail addresses where you could reserve in advance. So too did many hostals. In Spain, a hostal is like a one or two star hotel. Many seem to be run by a family. Generally, they are clean, private, safe and affordable. Sometimes breakfast and free Wi-Fi are included. The cost ran from a low of €25 to a high of about €50 for a single. Doubles cost less than twice that, figure on 1.5 times the cost of the single.
In fact, I have seen individual adults "combine" their housing needs to share a double. I hesitate to use the phrase "hook up" as it has a certain connotation. The point here is that you need not be traveling as a formal group or couple to share a room at a lower per capita cost. This said, all housing options along the Camino are highly individual. Whatever works best for you is simply that. It is your Camino.
As a 60+ fellow, I find myself a fungus and bacteria magnet in albergues. I get bronchitis rather easy too. So, rather than have these things detract from my enjoyment, I favor the hostal route whenever possible. Having a door that locks, clean sheets, extra blankets, HEAT, and a private bathroom are luxuries beyond price. Also, being able to either do hand wash and dry it in your room overnight, or give it to the proprietor to have done for €5 - 7 per load was also an appreciated luxury.
I also bring my 600 gm synthetic sleeping bag, just-in-case I end up "roughing it in an albergue. municipal sports hall, police station, church or whatever presents itself in extremis. BTW, these are ALL situations which have NEVER presented themselves in my two April-May Caminos.
FYI, I budgeted €50 per day for all costs, excepting travel to and from the starting and ending points. This seemed to work fine for me. I hit an ATM every 3-4 days for about €200 and never ran out of money. Hence the €50 per day figure.
I hope this helps.