Need somethimg to get me through the next few years

I co-own a small lawn service. Currently we are running two toro 30" walk-behinds and are looking for something to help is get yards done more quickly. I was thinking about just getting a ztr from Home Depot but now I'm torn. Here is what I'm looking for:

Something in the $2500 range
Something new because I'm not very mechanically inclined
No bigger than 42" wide
Something that will get us through the next few years while we save for a commercial mower.

We will probably be cutting no more than 20 yards per week for a while to come due to our full-time jobs.

Any suggestions?