Ok, time to get this forum back on track. (Some comic relief)
You all are disappointing me. You forget 'reasonable' justification is not what we do here.
This spring I'll be mowing 6 acres with a 4720 (Just traded my 3720 cab).
I Started out with a Craftsman GT5000 then a 2305 :O) - Oh, it's been a long road.
The point of us is to somehow justify (in our own minds at least) the BIGGEST, BADDEST piece of equipment we could possible use to get the jobs we have in mind done. Digging 30 post holes - that means you need a 990 or larger

Moving snow for a 30' driveway - A TLB with a hydraulic Skid Steer blower up front - Loading bark mulch in the pickup once a year - Maybe a high volume bucket on a 4000 series. heck, if it wasn't for weight maybe a 5000 series to blow snow and mow the lawn would be the right fit.
With the exception of pure lift capacity and the few jobs that require a lot of it, and my stump grinder I could do everything I do with my 4720 (or former 3720) with my 2305 just far slower (usually).
Anyway, now on topic, Seriously, it's usually about more than just dollars and cents but I do agree if it's purely mowing the decks (Well over 3K for a 7 iron 72") are far more than than middle quality pure mowers.
I originally mowed 6 acres with a 50" GT5000 (Still have it) and a 60" swisher side tow mower for about a 100" cut with overlap. I could mow at 3-5mph (depended on the grass length) with good cut quality without bagging. Probably just a little slower than my 4720 with an 84" RFM is.

When I had it I though about pulling two swishers for about 150" cut but that would have been extreme.
One thing also, is the Swisher unit I had had the best height adjustment I've ever seen. 4 wheels and 3 crank screws with vernier gauges on it. No pins, no deck flopping side to side scalping, etc.
If I was going for economy I'd go with something like that or a Zero turn if I had a lot of obstacles.