If you don't already know how, learn to cook.

Then take a stove and use it.

Alternatively, learn how to assemble cook-free meals... schedule a time of the day to collect and eat perishable foods from supermarkets or other stores. That will help reduce your food costs.

The rest such as accommodation, depends on how creative you are in free-camping or finding people to stay with on lists such as warmshowers.

The real answer, of course, is to jump in and start doing it with an overnighter, such as an out-and-back. As you learn what to look for locally, even scoping out by a motor vehicle if necessary, you'll get the confidence to go further afield. It's what most of the older hands here have done.

In doing this, you can record the costs of your trips, and determine at what comfort level you are happiest.

And that is the reason why it's not possible to give you an accurate figure... the comfort level you are happy to sustain is something that only you know. And of course, that has to be related to how much you can afford to spend.