Both of these should be fairly cheap and affordable.

That they wanted "Cheap" buys, not intelligent buy's, not data driven buys, not future casting buys, just "cheap". 

Throw your experiences in comments below; I'd love to hear success stories and/or horror stories!

You can throw some tents up about anywhere and rent them for something.

I'd look into sound reducing alternatives before you throw the baby out with the bathwater. 

Then throw up some security alarm stickers.

Building a separate one isnt cheap , I have run the numbers , with permits , nd the other county BS its close to $200K for an 800 sq ft building . 

Focus on absentee owners and start with the ones who live the farthest away and only own one property in the area since they have the least use for the property.You can also drive for dollars, looking for anomalies of disrepair and then look them up in the tax records and use a site like Spokeo to do cheap skip tracing.

Quote from @Zachary Kessler: Hello all I’m currently hacking my house that has an ADU dwelling that generates income, I bought this property intending to leave and rent the house that I currently reside in (2 bed 1 bath) I currently have a very good interest rate locked in here from 2022 that I don’t want to lose or have my mortgage called due from leaving here, I live here for very cheap with the income from the ADU.

Gas is usually cheap to run.