Before you go spending bucks use the onboards flash to trigger remote flashes as a try out/test, you might find that it works for you.
I use two flashes off camera -- the Sony 58 and 42 and they are quite sensitive to the the onboard flash. For many of the shots of that ABSA Cape Epic, which by the way are fantastic, the on-board system would have been fine. The 58 or 42 can also be mounted on-camera if the range needs to be extended a bit.
Give it a go, the system is already there, that way you have full metering, high speed shutter synch to the camera's max, ratio control between two external flashes etc already, all in full Auto mode if you want.