While I usually don't respond to anything written in that language ("tourism" in English and the rest in Sinhala) here's my tuppence.
It depends on several factors:
number of guests
itinerary
hotel type
activities requested
Let's discuss that later.
You don't need a license to take them anywhere as long as they are your personal friends. But if they go as tourists you will need a site guide at several places such as Sigiriya and Anuradhapura archaeological site etc. Those site guides charge a price, and then most of them force the tourists to pay a "tip." If they don't pay, they will be harassed and abused. So the driver has to set up the absolute final price on behalf of the tourists, and agree that no extra tip is paid. But most of the drivers cannot be found until the guide has ripped off the tourists. It's not an accidental missing, if you know what I mean.
Tourist drivers give you low rates depending on the country of tourists mainly. If they are rich westerners the offer will be around 60-70 USD per day.
The catch: He will flay the tourists alive.The itinerary will be full of "Sri Lankan experiences" such as gem shops, spice gardens, massage parlours, water sports, dance shows, tec factory visits, and a lot more. All of them give the driver a huge portion of the money they charge, plus a lot of free stuff.
A good driver (a very rare find, almost non existent) charges for these: cost per mile, his accommodation and food, road tolls, and around 15% profit minimum. And he doesn't drive them to spice gardens and village tours. He doesn't drive them to the Bluefield tea factory.
Getting a price is not doable without an exact itinerary and other details. Anyone who gives one will be asking for more money later.
