Consider using AirPlay Mirroring with Apple TV and a rented or borrowed TV set:
Use AirPlay to see your desktop on an HDTV
AirPlay Mirroring lets you send what’s on your Mac to an HDTV wirelessly with Apple TV. If your Mac supports AirPlay Mirroring, an AirPlay Mirroring status icon appears in the menu bar of your Mac when an Apple TV is on the same network as your Mac.
Before you begin, see the Apple Support article About AirPlay Mirroring in OS X to find out if your Apple TV and Mac can be used for AirPlay Mirroring.
You could also hook your Mac's HDMI output to the HDTV without the Apple TV but then you must stay close to the TV during your presentation.
thanks for the reply, but not all potential customers have a tv on its premises.
For now, I visit the potential client ... I hope that a future, potential clients come to my office.
I've used an Epson projector for the last 3 years for doing presentations and training. Cost around $500. I've been very pleased with the projector