It is very hard to sell low end laptops and make both the seller and buyer happy. I would say your minimum would be 0 and you should be very happy getting $25-50 for it. Sorry I can't help more, low-end laptops sound great in theory but they often just frustrate the user because of the lack of power they have under the hood. The real question is how much you are willing to tell sort of half truths like, "it is great for kids" and "if you only surf the web and play youtube videos it is great". Sure the laptop will do okay, but once it starts to age, get some malware, or more programs want to be installed, limitations will quickly catch up to the laptop.
In the end you could probably sell it for $25 - $100, but again it all hinges on how...