Let's say you paid $250k for it, and it's now market value $500k.

Depends on the market!

North Idaho has good markets if you are in Washington and Boise or Eastern Idaho if you are in central Oregon.

We own SFHs in Columbia SC and like that market.

We listed strategically and were under contract in 2 weeks in the slowest part of the year (December) whereas all the other similar homes in the neighborhood have been sitting for months and still sitting on the market. 

Higher DemandThe rental market is shifting.

If you are willing to live in urban areas you may want to talk to a local bank in your market and see if they have any incentives or grant loans for certain areas.  

in a stick frame market and one of the cheapest markets to build we build with margin at $190 or so a square foot. that will go up over time about 5% or 10% a year to keep up with new build price increases. we are buidling a 3 story walk up and source some of the lowest priced crews.

I realizing the duplex conversion strategy is more complex I probably wouldn't try it on my first property, just want to get a sense of what's possible in the Chattanooga market :) Thanks!

Chicago, with its vibrant neighborhoods and strong rental market, is a prime location for this strategy.