Having done a fair bit of research on this, it would seem that a number of "drivers" are out there to make a quick buck from the new wave of tourists that are planning on visiting the country. I've had a variety of ridiculous quotes emailed back for suggested 14 - 21 day itineraries, ranging from $1000 - $2500! This literally being for a driver and fuel - nothing else.
I'm all for people making a bit of money, but it would seem that these figures are being plucked from thin air, and without any thought other than to rip off unsuspecting tourists. I think sticking to the buses/coaches is probably the best way forward!
So you want to have a single driver for your entire trip? It really doesn't make any sense. Just find new drivers at each destination (and you don't even need drivers at some destinations like the beaches, Kalaw and Nyaung Shwe) also every driver that I dealt with was honest. The Intercity VIP busses, while occasionally late, are comfy and more efficient than you might think.
It made sense in that by having one driver, we wouldn't need to organise different drivers at different destinations, and being on a fairly tight schedule this sort of made sense to begin with. The VIP bus sounds like the best option (like you said) and we're going to use them.