These days I instead focus on cloud computing, specifically AWS. I scream at people to stay away from SES.
If he's gotten it working and deliverability is high, he will not see ROI from absolutely anything else he does.
I used to pitch in with SORBS, and helped run the SPAM-L and later SDLUS newsletters. I know what I'm talking about. It's an absolute bear.
In his shoes I'd pay $20K a month for that reach without blinking and still consider it a wonderful trade.