Do I need to spend $20 for a 5-2300 MHz 2 way Digital Splitter, or will a $5 5-900 MHz one do? This is splitting the digital cable signal from the wall and feeding a Shaw HDPVR and a FM receiver.

There is no such thing as a "digital splitter", outside of marketing. RF is RF and a decent quality splitter will handle either equally well. A junk splitter will handle neither well. The important characteristics are frequency response and loss.

But what freqency response do I need?

Digital cable operates up to 1 GHZ. (Although most cable companies are only at 800 MHZ).
Channel 125 is at 800 MHZ
Channel 135 is at 864 MHz.

http://www.jneuhaus.com/fccindex/cablech.html

The 2.4 GHz is for Satellite.

We always recommend 5-1000 MHz minimum and bidirectional. IF you have a 900, it could cause issues with the higher frequencies, especially on an 860 MHz cable system. You can purchase 2GHz splitters online for a few $.

Why not just get quality ones from your cable company? I get a couple of them from Shaw for free.