check your local craigs list and if you have a local for sale paper and see what is in there, that will give you an idea about your area. In our area chicks sell like hotcakes from Jan until about now then the interest drops off. We sell hundreds and hundreds every year, just from chick sales they totaly paid for 2 GQF Sportsman incubators, they pay the feed bill and then some during the season. Pure breeds will outsell barnyard mixes. Once again it depends on the area you live in and what's popular. In our area the Buff Orp and Rhode Island Red are king. You put an add up for Sussex or Cochin and people say "what is that" It's fun and you can make some pocket money off it, don't give up your day job to go into the business. lol
The only down side is dealing with some of the people. Most are easy to get along with and do business with. Some to be honest are creepy, when you put your phone number on a sale paper people assume they can call you at midnight, prank calls, lonely people that want somebody to talk to etc. My wife has always said if it wasn't for me being there she would not sell from the house and that makes sense if you are single or way off by yourself and hubby is working. There are ways around that, set up a table at your local feed store or something like that in public.
Also, you don't want to over hatch and have to hold on to the chicks for a long time, they will eat what they sell for. We time ours to hatch on Monday or Tuesday and be ready for sale that weekend. They are moving around well and eating/drinking so you are selling good quality and healthy chicks
Steve