Depending on where you live that could be a roadblock.You should research 1) city's website for any notices of permits/licenses/certificates you need to complete as well as any tax responsibilities 2) depending on local laws there may also be a lodging tax for the county (usually, but not always Airbnb/VRBO collect and remit these for you).3) verify that the zoning of the property allows STRsIn what area is the property you're looking to change to an STR?

I'm trying to get some idea of these costs and determine if it's even viable.County Reqs: Lodging License from State Health Dept (roughly $375/yr), Permit from the county ($275/yr), septic recertification, and water testing (well water) annually.

A couple of guys could do that with probably 15-30 bags of concrete mix and a day's worth of work.Gravel has a nice way of getting lodged into people's shoes and scratching up interior floors.

Plus, we covered lodging for them while the building was re-done and their unit was repaired with new sheetrock. 

Curious, are you under the impression that you are required to get a lodging permit with the state in addition to your city/local conditional use permit?

If it is allowable to do 2 STRs there, then I'd check your local competition by going on VRBO and AIR and see what others are getting for nightly/weekly stays.I don't think there is an issue with 'duplex style'....people looking for vacation lodging stay in hotels after all..IT may not have quite the same appreciation value as a typical house, but does that matter so much if you're raking in the $$ with STR guests?

The initial appeal of AirBnB was saving money on lodging.

After seeing how much we're spending on lodging (all AirBnBs), I'm re-evaluating where we rent from.

Hi Ben, I just did a little write up on an SRO we've had for ~5 years in the Deal Diaries area if you're interested in reading:https://www.biggerpockets.com/forums/850/topics/956944-high-cashflow-lodging-house-walkable-beach-community-s-of-boston

It may be a bit costly but an idea that comes to mind is you paying for a PODs so they may load up their household goods and you flip the bill for temporary lodging at a hotel.