21 x $100 x 12 x .5 x 10 = $126,000. So the price is high at $165,000. However, I think that you have to factor in the fact that the lot rent is absurdly low for the Dallas/Ft. Worth metroplex. In addition, you have to factor in the price to rehab the homes, as well as the fact that the seller is willing to do huge leverage.
If you go to the end of the movie and estimate that you can get 21 x $250 (more typical for rent) x 12 x .6 x 10 = $378,000 at the end of the project. Assuming that you can repair the homes for $35,000, then the deal stands to be able to make you around $180,000 or so if you complete all the work and stabilize the park. Turning $45,000 into $180,000 is not a bad thing.
But this deal is obviously complicated and you need to get a good handle on many things such as:
1) The market lot rents
2) Exactly how many POHs are vacant and what it will cost to rehab them
3) The results of a test ad (even though Decatur is in the D/FW metroplex, it's a town of only around 6,000 and I'm not sure of its desirability)
4) The interest rate, ammortization and balloon on the seller's note
5) The condition of the current infrastructure
The bottom line is that it may have merit -- I just don't have enough info. to say for sure.