2 drachms weight value

I've been offeren this interesting little piece for NZ$8 (around US$6, £4, or 5 euro) does that sound lke a fair price?  I like the thing but have no idea what the value is

http://www.trademe.co.nz/Browse/Listing.aspx?id=794455390

If you still hadn't figured out what this is yet, it's an apothecaries weight used in compounding and dispensing drugs.  Cool little item.

http://home.iprimus.com.au/davecoates/catalogue.html

Yeah I knew what it is, I just want to know how much it's worth.  I cant find that anywhere