A narrator? With only 3 or 5 seats available to pax, you couldn't afford to fill one with a narrator! You could use a recording instead. I took a pleasure trip across the Grand Canyon, and all that standard narriation was a recording on the intercom, with the pilot only pointing out things specific to that day.
If you were doing this in Europe, then remember part of your price is going straight to the VAT man! Albeit, you could claim back the VAT on your fuel, and purchase price of the aircraft (if applicable).
Personally, I think you would find it very difficult to make a living out of it, if only being able to accomodate 3 or 5 pax, unless you were doing it somewhere with consitantly good weather, and a good tourist trade.
Just because the weather is flyable, doesn't mean that a pax is going to enjoy being bumped around in turbalance!
Lets say you charged £40 per flight, on a 4 seat aircraft. That mean that in the UK you could keep £34 of that, and send the rest to the VAT man. So if you are luckey and manage to fill all three space seats, you have a turnover of £102 for the flight. Now take off the cost of your fuel, maintenance, engine fund, insurance and other costs (all with out VAT of course), and I suspect you'll have very very little profit if any. Then of course you'd have to take allowance of all the days you can't fly!
So therefore, either you need a bigger aircraft, which you need to be sure of filling, or need to be able to charge more!
dp