Anders:
Well, in a sense, it's worth whatever you paid for it at the flea market!
Unless there's something in the material that hints at its date of manufacture, it could very well be a brand new pipe. Currently, these are selling for around US$100. But without seeing detailed photos of it -- to see if there any fills/flaws/etc. -- I'd say it's probably worth US$50-60, maybe a bit less.
Savinelli is a respected name in pipes, but the 606 line is very easy to find -- both on eBay and brand new -- and it sits at the lower end (in terms of price/quality) of what Savinelli produces.
Bob