ADU

With the already qualified ADU, here are some numbers for you to consider:

There are several manufacturers, including Walmart, offering a two bedroom model for $23,900 delivered.
After accounting for setup and lot prep you would be in it for $26,000.
A single bedroom budget rental rate for Boise is $1,700 and a two bedroom over $2,000.
This means your break even point is roughly 16 months.
Thereafter you will be realizing a monthly income of between $1,600 to $2,200 for one unit, and this lot can accept two units, both with off street parking because of the rear alley access.