What market research have you done in regards to income levels, vacancy rates, market rents etc.There should be no need to offer any incentives if their is a market for the size of home you are offering.

Depends on size, leverage, and location really.

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. 

If their chart showed sales down 8% for February when the correct answer was plus 12% hard to ever listen to them again  Try to avoid “news” sites with “ad”(vertising) in the name  https://www.cnbc.com/2019/03/22/home-sales-make-record-jump-in-february.htmlHome sales make record jump, proving how sensitive buyers are to mortgage ratesSales of existing homes skyrocketed a whopping 11.8 percent in February compared with January, according to the National Association of Realtors.

@Brian S. there's a key metric out there with charting about the sustainability of a portfolio less than 50% leveraged vs standard equitys (which would be all cash)  and a real estate portfolio leveraged more highly than 50%.