Hi
You are right, a comprehensive reply would run to a book - several volumes

A quick review.
France - look for camping municipal or camping a la ferm, a night can still be had for around €10. Every town has a tourist office - tell them you are looking for budget accommodation for 1 or 2 nights, they often know someone that’s under the radar and a lot cheaper than a hotel. Eat in restaurants only at lunchtime, look for workers vans - evening meals are a lot more money. Avoid the coast if you want to save money.
Spain - the campsites are a lot more expensive but the food and drink is a lot cheaper than France, including restaurants. Unlike France the costal areas can be cheap for food due to competition.
Italy - campsites are similar or a little dearer than Spain but food and drink is more expensive than France. In general you pay for everything, even if you want to sit next to a lake
Eastern Europe - your money will go a lot further. Campsites are becoming more popular but if you’re off the beaten track you will see private houses with a sign in the window “Zimmer” this means room in German - just knock on the door and you will be well looked after
Balkans - only worth camping in Croatia (IMHO) but try to avoid the high season - traffic. For the rest, hotels are good and cheap - often the campsites are Dutch owned and more expensive than a 3* hotel. Definitely call into Motocamp Bulgaria
Germany is similar to UK.
Northern Europe, Scandinavia - expensive as you probably know. As the weather can be iffy there are cabins on campsites which are the best option. Often hotels will do an all inclusive deal where breakfast and evening meal is included which is worth seeking out if you’re somewhere for a couple of days - don’t be worried about taking a doggy bag to breakfast - fill your boots, the Scandinavians do especially the Norwegians
Wild camping is fine in Norway.

Enjoy