Real words and name prices are selective to whom ever may be interested in buying or selling. My suggestion would be to price your names at what ever you deem to be fair, and edit your shop deion to say that you're willing to haggle on the price if any catch their eye.
That way, the creatu are priced at what you deem fair, but it also leaves the door open for those that might want to haggle and feel like they get a deal on the transaction.
There are definitely some words/names that are considered way more valued due to how wanted they probably are, like say; Unicorn, Wizard, God, Magic, Jeff, Matt, Chelsea, Heather.
Said word or name types probably shouldn't be priced below say 500-600m.
And have fun with it, it can honestly be kind of fun to come up with some creative sales slogans to post in the shoutbox sometimes. Plus you'll meet some really great people who may be interested in some of your creatu.