Jason...
The Landpride side discharge 2560 runs about $1,600 new, and the rear discharge 2560 runs a little higher. Both are made very well and tend to hold up under heavy use. There's a big difference between a finishing mower like the 2560 and a rotary mower which is made for heavy un-finished type mowing. The rotary mower will typically have 2 to 4 heavy 1" thick steel pivoting blades attached to a center hub. They are made to withstand impact with heavy brush and rocks and the free swinging blades will bouce off things they were not intended to cut (theoretically) /w3tcompact/icons/smile.gif. I have seen rotary blades broken completely in half. Anyway... they are not intended for lawn mowing and don't make a smooth clean cut like a finish mower does. On the other hand, the typical 60" finish mower has three blades similar to most walk-behind lawn mowers. Each is attached to a belt driven spindle mounted to the mower deck and driven through a gear box by the PTO. The blade tip speed on a finish mower is in the neighborhood of 10,000+ RPM, and a rotary mower is considerably slower since it does it's job with weight rather than speed.
A light to medium duty bush hog should handle saplings up to about 2" or a little larger. At least that's been my experience. The larger the sapling the more tearing effect you'll get from the bush hog. The finishing mower on the other hand makes a cleaner cut, even on a small sapling, but will also tend to bog down and tear if you get into more than it can handle.
The best bet is to have both pieces of equipment. I'd prefer not to be sharpening blades constantly on my finishing mower. Plus... if you allow your rough stuff to get a little too rough... then you're going to end up having to borrow a bush hog anyway. It's just nice to have the correct implement to handle any particular job. And your mower is like anything else... if you can find a good used one for less money it should always be an option.
Hope that helps some.
FarmerBob