Huh. Well there must be something, or else why are they charging those extra $27... Aha, just checked their website. Seems like the $50 version will contain the forms you've sent to IRCC and will be the "complete file from CIC", while the $23 version is "file as is". My $23 notes do not have the forms I submitted.
This is actually the document that, as the name suggests, verifies your PR status (and not the PR card, which is just a travel document). The CoPR will be signed by an officer during landing, and is very important, you'll need it when/if applying for citizenship.