Not in historic district permits should not be a problem.

We successfully permitted and are in the process of building a bonus ADU project.

This is one of the few things Baltimore City Government actually does efficiently - probably because there aren't people in the loop.Log into your Baltimore City Department of Housing & Community Development online portal, click the "My Account" at the top and then "Permits & Docs" on the left side.

No drawings were ever submitted to the city and permits were not applied for until February.

It may also include submitting the requisite permits to support your plan.  

What will happen to illegal airbnbs where permits dont exist?

I know here in Denver, the city has cracked down on short-term rental permits for unauthorized basement units. 

Does anyone know how much is the minimum that I can realistically pay for permits, plans, materials, and labor?

I'm aware that's a great market for STRs (regulations permitting) but didn't know about the new MTR demand.

We also currently have 2 more ADUs that we just submitted for permits to city of San Diego.