DISCLAIMER: SUNN SERIAL NUMBERS HAVE ABSOLUTELY NOTHING TO DO WITH DATING. THE BEST WAY TO GET THE DATE ON A SUNN AMP IS TO PULL THE AMP CHASSIS OUT AND LOOK FOR A DATED INSPECTION STICKER OR A DATE GREASE PENCILED ONTO THE BARE WOOD OF THE ENCLOSURE OR SOMEWHERE ON THE CHASSIS WHERE THIS IS BARE METAL.
And in "today's market" a silver face solid state Coliseum is worth about $300-$800 depending on the model and condition.
Do you have verified sales, such as warandhairstyle's completed eBay auction to substantiate those numbers? Or is $300-$800 just a number you are guessing at? I think it's a good idea to keep price speculation "real", a lot of us keep track of
actual sale prices, which is really the only way to accurately judge market value when
real money is being discussed.
If you boil it down, a used item is "worth" exactly what someone paid for, no more, no less, and guessing at "value" when there is no corroborating evidence is misleading, and generally inflationary.
And... none of us want to overpay for an item based on someones unsubstantiated "guesswork", or want to short sell a nice piece of gear for the same reason.