You were right in saying the prices are too high....especially your opportunity cost. You could essentially buy more property and almost double the cash-on-cash return (COCR) by investing at a lower price point.
Based on the info you provided, it sounds like you have around $100k to put down while carrying $300k in debt service per property. Correct?
If that is the case, the initial numbers don't support a scalable investment strategy. You could essentially buy an extra duplex and double the COCR with the same $100k available cash you have by investing in 250k-300k duplexes.
My duplexes are in the western metro suburbs and rents are $1200-1500 for my 3br units. My Robbinsdale duplex rents for $1250/unit and I bought it for $195k.
As an agent & investor, I'm viewing duplexes in western suburbs (Hopkins, Crystal, Golden Valley, etc) going between $230-290k with rents in the range you listed for the 400k properties.
So...yeah...to me...you are right in saying it is too high. I would stop and think about what is an acceptable rate of return for the cash you invest and select price points that allow you to get that rate of return.