while I think its possible to do a skoolie on a shoestring budget, alot depends on how much you are willing to and then re-do later.. and how comfortable you want to be / how much time is spent travelling vs parked..
if its a casual RV that you want to have for summer road trips, hunting outings, fishing camp, etc.. then the idea of building a minimal but not necessarily energy efficient / off-grid skoolie works better.. ie for a few weeks out of a year its feasible to buy gasoline to run a generator for A/C vs expensive solar.. ie twice the propane so you can heat with minimal insulation isnt a big deal.. a mechanical breakdown isnt the end of the world.. it can be dragged home and sit for mnths if needbe..
put in a cheap floor now then you can take the bus apart later for that nicer floor if time and $$ allows when its a weekend RV..
going about full-timing is different, esp if your nomadic lifestyle is you liveliehood.. you depend on travelling where the work is.. a broken engine all the sudden threatens your income... so its imperative to learn mechanics, buy a bus that is very solid.. (or pout some $$ and time into the mechanicals before you convert)..
when full-timing its a LOT tougher to re-gut your bus after you have left your hoime-base and made the bus your home-base.. using harsh chemicals for insulation , painting, etc needs to be done when you arent already living in it... obviously this increases upfront costs as this scenerio looks more towards doing things tight the first time as oppose to "right now"...
monthly outlay of costs varies greatly with the lifestyle you maintain... 6-8 MPG adds up quickly if you must travel in your bus alot for your liveliehood. propane. generator fuel, etc if you are the type that doesnt want to live like the 1800s.. (you want thiunbgs like heat / AC, modern liughts, internet etc..) all can cost just as much as it does living in an apartment.. however obviously you are much free-er when living in a skoolie to rtelocate, travel to where work is, etc..
for reference the Used RV market is pretty low right now.. buying a used RV can easily be more cost effective than building a skoolie.. esp for those building shorties.. (class C RV's go for pretty reasonably.. even brand new..). however building your skoolie, you get a much more robust and stout vehicle, as well as the ability to build exactly what you want into it... nothing less and nothing more... along with much more capability for those into off-gridding.. no commercial RV's really come with any serious solar or wind capabilities like can be built into a skoolie.. nor a wood / pellet stove either..
as for costs.. for those who just plan to have a bus and park it in one spot.. unless you own your land, its not necesarily cheaper than living in an apartment... for instance an acquaintence of mine went through this recently.. he has driven and ridden in my busses and thought wow!! get a longer bus, convert it, live in it and ditch the apartment rent...
till it came along to find and secure parking that allows residency, fuel to drive, fuel for heat / cool, laundry, water, insurance, mobile internet.. turns out if he simply moved 35 miles west of the city proper he found low-cost but nice rentals.. .. some are newer / efficient, and the costs were very similar if not a little better overall.. he doesnt own it but he is comfortable..and can consider a skoolie for a weekend RV.. that he can build next to his rental house.. a beater corolla to get to work, and he cut his monthly cost more than 1/2 of what it did to live in a nice apt downtown... his goal was to cut costs by 35-40%.. so dont always look at just a skoolie to cut living costs..
-Christopher