Just to give you an option, I would look at that Gravely XD3. I do not have one yet but it sure is impressive for 400.00. heres a link.
Gravely XD3 Walk Behind Lawn Mower
Check out the video in the video section. I hope that helps you. If your going to grow your business, go ahead and get yourself a proper commercial mower. I got the entry level Gravely Pro Turn 52. I love it! Good luck with your search, there are tons of excellent choices.