There are also software apps that will run on a pc/laptop that can add the 'live accompaniment' capabilities of an arranger to a workstation. One Man Band (OMB71) is one that I have worked with, and it seems to do a nice job. If you already have a pc/laptop with a MIDI interface to the workstation, this may be an option for you.

What you lose with the software approach is the "all in one; dedicated buttons; easily portable; fast setup" advantages of the arranger boards. These aspects can become more important if you are doing live gigs.