There's a thread here: >>1066260 with answers to most of your questions. Reading through it would probably help.

But to start off with, make sure you didn't pack too much. You don't need much to walk to Camino. At all. If your backpack is over 40-45 liters, it's probably too big, and if you're carrying more than 10kg, you could cut some stuff out.

It doesn't cost very much. Basically the Camino costs as much as you want it to. Most of the time, you can find accommodation for around 10 euros or less, and the only other major expense is food, which can be quite cheap. Eating off the menu del dia is filling and usually costs 10 euros, fruit and other food can be found along the way in markets for cheap, and food in small bars is also usually inexpensive. Wine and beer are generally cheap. Most people say 30 euros a day is pretty typical, but it's possible to go cheaper (depending on how much you eat and drink).

A small note about price, though. Some albergues are "donativo," which means you can pay whatever you want. That doesn't mean it's free. You should pay about what you would normally, and maybe more if you really liked the place. They can be great places to stay, and someone has to support them.