If you like them and are going to build sites on them, then they are worth whatever you think they are worth to you.
If you are looking into buying them to sell, take a pass on these. It's gonna be hard to find a buyer for them. It doesn't matter if the extension is fun or catchy, they just have little value right now and more than likely, for a long time.
Like I said, if you are wanting them for yourself and are going to build sites for yourself, then the value is as much as you are willing to pay. If that's the case, you should be able to get them in the low-mid $xx.