A commercial stand up will be just as much over kill. The stand up or the walk behind will cost in the $4000 to $5000 range. Commercial mowers are built to get landscapers in and out of jobs fast so they can get more done in a day. If you are willing to spend that kind of money for a half acre why not get a small deck ztr? The mowers mentioned earlier are good options. I have the snapper pro s150xt 48" and I mow 4.2 acres with lots of trees, hills, and some rough spots. The icd deck cuts great. The s50xt is smaller than my mower, but the icd deck is offered on it as well. There are plenty of other options out there. There are residential ztr mowers with smaller decks as well that may suit you fine (craftsman, john deere, toro, husqvarna, bad boy, snapper, etc). You can find these at box stores and save some money. Should be able to get one in the $2000 to $3000 range. Decks will be similar to what you have though.