How much should you offer?
The last (used)however in fairly good condition gold plated Kirby auctioned on eBay about a year and a half ago ended up fetching $325 / $345 I believe it was a gold plated G4 - G5 And no attachments. I stopped bidding at $300.00
A vacuum like anything else is only worth as much as someone is willing to pay for it. The gold is only electroplating. So again, it depends on the overall condition and how bad you want to add a gold color Kirby vacuum to your collection.