About $30 a month off of AdWords for a fansite I run; it covers about 2/3rds (if that) of the server costs, so I'm content with that. I could earn more if I placed more ads, better ads, worked actively on the site / promoted it, but it's a fansite, and I think it'd be unfair for the people that actually spend obsessive hours writing content for it - if I were to make big money off of it, or would sell it (it's probably worth a few thousand due to content + google rankings), I'd have a massive headache and drama trying to distribute said money.

Effort is relatively low, a few weeks of on and off work to get it online, styling, moving servers a couple of times, etc. I need to move servers again I think, or at least upgrade all the software, it's kinda wonky for some people at times.