You can use free IFTTT.com to notify you when ads with a specific word or phrase is posted to Craigslist. IfThisThenThat https://ifttt.com/create/if-classifieds?sid=2
Create a free account there, then create a new "Applet". The "service" you want is called "Classifieds". You will need to manually search Craigslist (enter your search term; "beehive" or "extractor" etc etc) for what ever item you want, then post the URL/link for that Craigslist search into the right place on IFTTT, and tell IFTTT you want an email / text / etc when ads meeting that search criteria are posted.
It works quite well. Just pay attention to your search phrase so you don't get flooded with notifications of unwanted items.