I also do a bit of affiliate marketing on the side. It's not much, but my site just crossed $1k/month December. I've worked about 20 hours on it since this year. My total investment on it is about $800, excluding my time.
Do you mind leaving your mail address? If those returns are stable and you want to sell (in the future, too), I would like to talk. Many others here probably too.
Not looking to sell right now though. This site is in a field I have more than an amateur interest in. I plan to stick around with it for a while :)
1. Great content + organic backlinks. It's slow and takes skill (especially in content ideation and creation) but the results will be enduring
2. Great content + cheap, paid backlinks. This one is much faster but requires a budget and there is a substantial risk that Google will simply shoot down your rankings
You can't compromise on content though