In comparison to secondary storage, the primary storage is:

Compared with secondary storage, primary storage is faster and more expensive per unit of capacity.

Being close to the processor, it delivers data at the speed the CPU needs during processing.

Saying it is slower and less expensive matches secondary storage such as a hard disk, not primary memory.

Saying it is faster but less expensive is wrong, because that high speed comes at a higher cost.

Saying it is slower and more expensive combines two wrong traits and describes nothing real here.

This is why a machine keeps only a small fast primary memory but a large cheap secondary store.