Which airlines fly from Upington to Nelspruit
This is one of the least popular flight routes (in terms of demand) in South Africa. As such not a single airline flies the route directly, so if you need to fly to Nelspruit from Upington, you are going to have to fly with South African Airways via Johannesburg airport.
Typical prices for flights from Upington to Nelspruit
If you are wanting to fly from Upington to Nelspruit, I hope you are doing it for business purposes, as the price is going to be quite high, regardless of when, or how early, you book the flight. A typical price for a flight from Upington to Nelspruit can cost you almost R6500 per person return. The reason of course, being that you need to fly via Johannesburg, in order to catch the second leg of the trip to Nelspruit.
How to get cheap flights from Upington to Nelspruit
Unfortunately there is no real way to save money and get a very cheap flight from Upington to Nelspruit. The only thing you can do (and this applies to all indirect domestic flights) is to try and book the 2 legs of your flight separately. So book the flight from Upington to Johannesburg, and then book the flight from Johannesburg to Nelspruit.