I've got an NH LX 565. I bought an old 60" bushhog with a good, solid steel deck, stump jumper and heavy duty gearbox and went to work. Mower cost me $125 off Craigslist. Bought about $150 worth of steel plate and stout square tube, and a heavy-duty 3/8" steel skid steer quiktach mount for $300. Had an old 4.5 ci hydraulic motor laying around, and Surplus Supply provided the fittings, hose and cushion valve. All totaled I have about $1000 in it, not including a day or two of cutting and welding.
The thing's a beast. Having the mower in front of is great, and I've not really had any problem with rocks, branches and stuff being thrown into the cab. Cuts through 2-3" saplings like they weren't there. Waist tall grass no problem, though it will shake a little bit in real, real heavy stuff, but a little bracing with take care of that. Wish I had done it years ago.
If you don't weld, you could probably pay a guy for a day or two, and still be well ahead. Works every bit as good as the commercial units I've seen.