I bought a used Grasshopper front-mount 729BT with the 29hp Vanguard engine, and I have been completely happy with it. It only had about 220 hours on it and was 1/2 the price of a new one.
I'm looking for a 2nd mower now, so I'm somewhat up to date on what's out there. Here are my thoughts:
1. Don't overlook John Deere's 9-series zero turn mowers. Such as the 915, 920, 930, etc. You might be able to get into the 915e for just a little over your budget. A lot of people claim the 7-Iron Pro deck is as good as, or even better than, the Velocity + deck on the Scag mowers.
2. Stay away from the box store junk. But you already knew that.
3. If your land is rough, pay heed to Gary Fowler's recommendation of the Ferris. Due to the suspension, they ride better than any other mower I've tried. I tested a Ferris IS2100 back-to-back with a Scag Cheetah with the suspension platform, and it wasn't even a contest. The Ferris was like riding on a cloud. The IS700 won't ride quite as nicely as the IS2100 (which had full four-wheel independent suspension), but it will ride much better than a non-suspension mower.
4. Finally, a good dealer is just as important, if not more so, than the brand of mower you buy. Every brand can have an issue from time to time. You can buy the most expensive model that Scag or Deere or anyone else makes, and if your dealer doesn't have the knowledge or right attitude to service it timely and correctly, you're dead in the water.