I own a 52" Gravely zero-turn with a Kawasaki - love it.

I would suggest buying a used commercial mower. That will give you bullet proof hardware that will last forever, and be within your budget.

You may also look into a commercial walk behind mower. I have a 48" Scag, also Kawi powered.

I also mow 1 acre; the zero turn goes over the ground faster than the walk behind, but by the time I mow around common obstacles, the walk behind is faster overall. Also, with a zero turn you have to be very careful when making zero-turns...the large rear tires will scalp the grass right off. My son and I call that "making dinner plates".

Best of luck in your search.

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1992 500SEL 25K
1995 E320 40K
1995 SL600 120K
2002 JX8 Sport 43K
2005 Volvo S40 95K
2006 Isuzu NPR 304K (Frankencamper)
2007 Crown Victoria 150K
2014 Smart Electric 20K