What is the value of a Nightrider compared to orthodox chess pieces?

I'm guessing 5 pawns...

I've heard that it's about 4-5 pawns (stronger than a regular knight, but somewhat weaker than a rook) 

Actually it turned out to be about a quarter of a Pawn stronger than a Rook, in my tests.

HGMMuller is probably right. Nightrider is a major piece. 

But king + nightrider still cannot checkmate a lone king, so nightrider is weaker at least in this aspect.

It's difficult to say because the name "nightrider" has very low creative value. We already have a knight.

What are you trying to say?

Indeed, Nightrider has no mating potetial, unlike Rook. But mating potential only contributes little to the value of a piece; most ed-games in Chess have Pawns in them to provide the mating potential, and it is much more important how well the piece supports or hinders Pawns. There are pieces that are far stronger than a Rook, yet have no matig potential. E.g. a piece that could teleport to every square of the same shade as it is on.

is camel rider has the same value?

Depends on the board

In 8x8 its terrible

If we were focusing on checkmate then r>n+n

So checkmatin isnt our focus

On a infinite chess board it would take three nightriders to checkmate

Around US$ 35,38 in the Black Market.