If it's really a Deere 175, I think he's a decade off on the age of that unit (1987-90 production run):
www.tractordata.com
At least it has an Eaton hydrostatic and not the dreaded Tuff Torque K46 (google that one and you can read for weeks). Deere definitely made heavier-duty units back in that time frame, designed by the same folks that also designed farm equipment which gets the living snot beat out of it.
Still, that's a 30-year-old machine at this point. I'm daily-driving (so to speak) a 1990 Deere F510 with the same 14hp Kawasaki engine on it, and it's got 770 hours or so and still going strong. I bought it for $300, and then had to do a full deck rebuild and tuneup on it when I bought it (think was around $500-600 in parts all total since I used OEM deere $pindle$ and idler$), but now it runs like new. Had I brought it in to do all of this work, it easily would have cost me $1000+ on top of what I paid for the machine.
I agree with other poster above that your Wheel Horse may definitely be worth keeping going. Unless you need a new transaxle or the frame is rusted in half or the deck itself is rotted away, I'd seriously look at what it needs - if you post back here with more details of exactly what is wrong with it, that would be helpful to give you correct guidance.
OTOH, if the Deere is in excellent mechanical condition (all blade spindle bearings, idler wheels, and other bearings smooth and quiet when you turn then) with good blades, belts, clean fluids, fully tuned-up, tight steering, it starts up quickly, runs smooth and doesn't smoke, $600 isn't a bad price for what you described.
Oh, if you are test-driving any used, older hydrostatic tractor, the acid test for the transmission is to get the fluid nice and hot and then try to drive up a hill. This may require 20-30 minutes of operation. Cold transmission fluid has much higher viscosity than when hot, and this can make the difference in a worn transmission whether it will pull a load or not. That was the big issue with the non-serviceable and undersized K46 transaxle - you would get a few hundred hours on it and then it would not drive uphill when hot.