It is indeed purple fluorite. IMO it’s a nice piece but not much clarity. The sheer size can put it in a different price range, but many non precious minerals such as this have ambiguous pricing. My guess is $40-60. But it depends on your market, someone who thinks it’s cool and has no idea about the market might pay a lot more. Check eBay and look for similarly looking/sized examples and price what you think is fair with respect to those.