Starting at 10c CPM, if every user viewed one ad... $405, most sites have 3 ads per page so $1200 if every user logged in during one day.
Better targeting and click through can get that CPM up, most places I know of managed a consistent 40c through automation, through sales teams $20 is achievable (big diff between google and agencies huh).
Now the real trick is how many pages does each user view per visit, and the daily visitor rate. Going off a user visit per month and 3 page visit. (((((400,000 users) * 3 ads)* 3 pages)/1000 cpm) * 40c) = $1440 from basic impressions without including click throughs and targeted spends...
Not much for a month unless you are in an area where the bidding is high like travel, I've seen travel ads going through at $20CPM, at $20CPM the above calculation is $72k.
So a huge range in profits, I would assume music sales would be a highly bid on thing, so maybe $30-50k a month ?