What is your best guess as to the income (from recordings and live
performances, net of expenses related to those) of a pop musician at a
given level of record sales & road popularity? i.e., someone selling x
CDs a year would earn roughly n per CD, and would earn X% of gross
receipts. Assume a younger but established artist (can fill a 150 cap.
club 200 nights a year, i.e., Richard Buckner or Cat Power) Don't let
the precision of the question bog you down, I'm really just looking
for round numbers.

In essence, the exact percentage of CD sales will depend upon the
contract agreed to by the artist and the music company (10-20%). 
Further, if the artist is not the composer of the music on the CD,
this reduces the royalty amount because proceeds are paid to the
writers of the music.

I found this sample recording contract online, you may be interested
in it:

http://www.order-yours-now.com/samplerecordingcontract.htm

And though this article makes my contribution here redundant, this has
everything you want to know, and takes the Smashing Pumpkins as an
example:

http://www.epinions.com/inst-review-5D3A-A5F084B-39C03D36-prod1

Thanks