Switching a SPI chip between two devices?
I would recommend searching for buffers (or line drivers, transceivers) with tri-state functionality.  Here is one example from NXP.  They cost $0.57 USD each at DigiKey.

Basically, they act as simple buffers, but you can cause the outputs to become high-impedance and effectively disconnect the signals from your circuit.  You would use two of them; one to connect (or disconnect) each of your devices.  It is made easier because SPI lines, unlike I2C (for example), are each unidirectional.

There are hundreds of different ICs to choose from. For example, some have a single "Output Enable" (OE) line for all of the signals.  Others have multiple OE's, allowing you to turn on/off only specfic signals.  Some are inverting, some aren't, etc, etc.  The architecture you need will depend on your specific circuit.

One thought: Perhaps you only need to switch your CS and WP lines?  You may be able to leave the rest of the bus (including power) shared between both devices...

Good luck :)