The guru your son is learning this technique from is likely not telling your son that the deal will almost certainly encourage your son to get an "off-market" deal from a "wholesaler" who is unlikely to properly disclose the details of the property or encourage an inspection. 

Like most markets, there is a growing trend in the area due to affordability and increasing more things to do. 

@Martin Manning To add onto what others have shared, in the most simplistic terms, apartment complex values are based on Net Operating Income, or NOI, and the cap rate.Price = NOI / Cap RateSo, if an apartment complex has an NOI of $100,000 and a market cap rate of 10%, the value is $1,000,000.Listing agents for complexes love to price based on a pro-forma, which is utter nonsense (unless you're in Austin, in which case apartment complexes apparently have floors made of gold).

Are you proficient on market research and analysis?

You can contact some local property managers and get a better idea of the rental market.

Study the market.

Personally, in this market, I would work on saving up and really doing my best to find a great opportunity and pull the trigger then.

Quote from @Mo Karim: How are the Milwaukee burbs market?

Hey Jerry - Tulsa and OKC are both booming markets and ones that drive the most demand in Oklahoma.

There's no precise figure because no one will understand your STR or market as well as you do- or, as well as you will (with time).