There are lots of people who are both boondocking in rural areas on BLM/NF land as well as those living in more urban areas. There shouldn't be much difference in their expenses - gas may be a little cheaper in urban areas but groceries are sometimes more expensive out in the boonies and it costs more to get to the market.
Instead of trying to work from someone elses' budget, IMO, the better way is to figure out your own budget.
Start with your income. Then list all the bills that have to be paid no matter what - insurance, cell, car payment etc.
The difference is what you have to work with for food, laundry and travel costs etc. etc. as long as you have no debt payments like balances on charge cards.
I just recently sat down with someone who, while they had sufficient income normally, had so much credit card debt that they were paying the minimum on each card and then using that during the following month. Essentially, they would never be out of debt EVER.
We worked out a plan that will have them be debt free within a year.
Ended up with $150.00 a month f.or food and only $75.00 a month for gas but since they drove a reliable economical car it just meant that there would be no long road trips. They would have to plan for up and down in elevation to move with the weather.
$150.00 a month is entirely do-able for groceries if you don't spend money on fast food and shop carefully.