Take a look on craigslist or on the marketplace on here and find yourself a nice used machine. This way you can get a quality commercial machine for far less money than buying new and still get quite a bit of time out of it. I took a look on craigslist in my area found quite a few choices in used commercial machines...I'm sure that will be what you find too.
There are plenty of brands available, just because someone on here doesn't particularly like one brand doesn't mean that it isn't good. Any reputable brand like Deere, Exmark, Toro, Scag, Hustler, etc., will serve you well. Just be sure to consider the dealer support in your area should your "new" mower need servicing or parts.
There is absolutely no need to spend you entire budget just to get started. There is plenty of used equipment out there that will serve you well as you start out and still keep some money in your pocket.
'07 Chevy 2500HD
2010 John Deere Z925A 54" MOD
2011 John Deere Quik Trak 647A
John Deere walkbehind