For $4-5k Look at the Hustler Fastraks, Scag Freedom Z (little about 5k), The new Kubota mower coming out, and the Gravely HD mowers.
Any of those are 100000000000000000000x better than anything you can buy at Lowes, Home Depot etc and will last much much longer.
For 3 acres a ZTR will run circles around a tractor mower and will get you on and off the mower in a fraction of the time. Unless you like riding a mower for hours on end, a ZTR is the way to go.
Hustler Fastrak: $5300
Scag Freedom Z: $5k
Kubota ZG series: $4500-$5500
A 48" ZTR would cut your 3 acres easily, for the price difference to go up to 52-54", it is not worth the price, as you will make a few more passes to account for the deck difference, no biggie.
With regular oil changes, air filter and fuel filter - the above mowers should last a long, long time, vs 3-5 years for the el cheapos at the big box stores.