I work with almost 150 investors/clients, most of which are out of state, who have properties in the Indianapolis metro area and would be happy to answer some questions and put you in touch with some people who may be able to help you determine your best direction, but there is no "one size fits all" approach.

For example, worth 75% of two single family of same size/beds/baths?   

I came up with 15K because my current flip will run about 50k for a home 3 times this size.

The property has a small 522 sq foot SFR that is designated as an HPOZ contributor, and our client is looking to build a new modular home about twice the size on the large lot and convert the existing SFR into the ADU. 

It comes out at $3,347 per unit which can be on the low side but it will depend on the size of the units.

How is the land zoned, what size lots are allowed in that area. 

Even at 10 bucks a foot 400,000.Typically with retail the larger the building size the lower management fee.

@Suthy MaxwellYou say nothing about the location, unit size/types, condition, etc., so how can we advise?

Be sure to look at items besides radios too - TNCs (radio modems), power supplies, antennas, rotators, towers, boxes of tubes - especially those the size of a tennis ball or larger - those can be expensive high-power tubes, which we still use in linear (power) amplifiers. 

@Brittney Butler for a property that size I would build relationships with local community savings and loans banks, in the area you plan to invest, that specialize in financing this type of product.