Buy it now?
But it's FREE...

Well, downloading the game on GOG is still handled like a normal transaction, sans the money, I think the button said Buy,
I have a CD copy of BaSS, bought way before it was freeware'd. It's just a White Label re-release with French CD inla, so it's nothing spectacular but if you happen to find an original with the comic book and all, by all means it's worth buying. Provided the seller isn't an a-hole trying to screw you over with an unreasonable asking price.
In the meantime, download away and GOG is a great source since you do get the comic book (which I didn't with the re-release), albeit in high resolution, printalicious PDF format.