I was in your shoes about 10-years ago. I didn't want to break the bank but wanted to get a zero turn for our 6 acres of mowing. A good friend of mine at the time worked as a dept manager for a local rental company. I was pretty much all set to buy a new Toro Time-cutter thinking new with a 3-year warranty would be the way to go. He talked me out of the residential grade zero turn and told me I'd be much better off with a good used commercial mower. By the time the warranty runs out, the residential units are ready for the scrap pile and are expensive to fix if you use them much. He said by 500 hours the hydros are weak, and the overall build of the machine just isn't there, and the majority come with cheap stamped decks. Said a good commercial unit will go 3k-5k hours with decent maintenance. This cost him a sale because they didn't have any good used commercial units. Ended up getting a lightly used Gravley ProMaster 152Z and put 500 hours on it with nothing more than regular maintenance, a couple of belts, and 2 deck springs. After 10-years it still looked and worked fantastic. Just sold it to buddy and made the jump to a Gralvey Pro Turn 472 a couple of weeks ago.
I'd say find a good used commercial unit and don't look back. There a several good brands out there and they all have their pro's and cons. a few good names in the commercial sector include Scag, Exmark/Toro, Deere, Hustler, Ferris, Grasshopper, Dixon, and of course Gravely. find something with less than 250 hours, have it serviced up, and you'll be good to go for many years.