Aircraft positioning adds the cost of getting the aircraft to you, and often back again. Unlike an airline, a charter operator does not run a network of linked flights. A charter aircraft sits at its base until someone books it. Then it has to fly to the passenger.
Say you fly Mumbai to Goa and the aircraft is already in Mumbai. You pay for Mumbai to Goa, plus whatever it takes to get the aircraft home. If the same aircraft type is based in Delhi, you also pay for an empty Delhi to Mumbai flight before your trip starts. The aircraft is the same. The price is not.
This is why a one-way charter is not half the price of a return. On a return, the aircraft carries you both ways. On a one-way, it flies out with you and back empty. That empty return usually appears in your quote.
It is also why being flexible about the airport can pay. A second airport thirty minutes further by road may have a suitable aircraft already there. The positioning you save can be worth more than the extra drive, sometimes by a lot.
Positioning also creates empty legs. When an aircraft has to reposition anyway, the operator would rather sell that flight than fly it empty. That is why empty leg prices look oddly low. The flight was going to happen either way.
Two simple steps help. Ask where the aircraft is based. Then ask whether the quote includes positioning both ways. A quote without positioning is not cheaper than one with it. It just covers less of the trip.