^this^ and you have 40 k visitors and 100k pageviews? and you make only 40 a month in total? I would keep it and try different offers, play with it.how long have they consistently been earning $40 ? if its steady and has been for months then they should be worth 10-12X the monthly revenue. If you have a steady flow of that $40 for longer than that then they should be worth a bit more.
judging By the stats I would say it is worth around $1500 or more.