The last nice condition and fully working Quantum to sell on eBay, that I know of, went for $3200. That was last year sometime. It had a WG6100 monitor.
I was offered (unsolicited) $3000 for mine (w/ WG6100) not long before that. Turned it down. I haven't seen an original Quantum change hands lately so I don't know what the current going rate is. I'd say add at least $200 for a working Amplifone monitor though.