The following site has a monthly cost log broken down, you may have to search a bit for it.
Monthly Travel Expense & Cost Log for Full Time RVing | Technomadia
It doesn't reflect what my expense log would look like but it does give you an idea of what to include when creating your own
Actually.....only you can answer what it would cost you (chances are it will be higher than what you are paying now).
What will be the cost of a place to park?
Fuel & Insurance cost for bus?
Does this include electricity, gas, water, sewerage?
Do you plan to have a TV service, Internet service?
Cell phone cost
Basically the same you have now minus what you are willing to give up.