It sounds like you are holding all the cards. My guess is that you would prefer to buy the place you are currently in (for a fair price).
If the market for your rental condos is in the $450K range, then offer the owner 440 and do the transaction without any real estate agents. You save on moving costs. He saves the real estate agent’s fees. You have a good idea of the property already and you could pay a lawyer by the hour to help with paperwork.
If he says no, show him the sold comps. In my opinion there should not be that great of a disparity in condo prices and he will eventually learn that his condo is not special (and you will learn that people won’t sell a huge amount below market). Until he realizes that, keep renting at half price.
If you are really an evil person at heart, tell him if he does not accept your offer, you will not allow him to show the property anymore, stop paying rent, and become a holdover tenant.
