anytime anyone asks how much it costs to travel in any type of RV, I ask how much does it cost you to live in a house? basically how much do you spend now and how will that change? Things like property taxes, homeowner's insurance go away but are replaced by more fuel costs and at least some campground costs. Look at the other stuff you already pay for like food and entertainment will that go up or down? Don't forget to keep a rainy day fund if that $4K unit needs some repairs.
some people can live on next to nothing while others "need" at least $2K a month to just "survive".