One consideration is the grade of the mower you're buying.  It seems like anything below the lowest commercial grade is very light duty and below what you'll be used to with your GT275.  We had a 275 and it was a great mower.  We went to a Deere 925A 60" and its slightly heavier duty than the 275 in my opinion but below that I don't see the durability.  Local Deere dealer did have a sign on a 1023E tractor only for $8900.  So if you had other uses for it that would be a good value.  I personally like a zero turn and Dad and I share his but if it were just me I'd have a compact tractor with 72" belly mower so I could use a tiller with it.  Mowing time would likely be a little more but it would have more than one use.