Look on ebay?
We've got a Rice cost us about £500, but wasnt that good condition. Depends about the condition, tyres etc.
Not sure about weight sorry
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About £1000 for anything over 15 years old. 10-15 yrs old probably 1.5K to 2k, maybe a bit more. Less than 10 and you would be looking at about 2.5K-3K as they hold their money well. They bottom out at about £1000, if they're in good working condition. You can tell its age by the size of the tyres and the rollover brakes. If the are the bigger ones and it doesnt have rollover brakes then its over 20 years old. Even so if its been well maintained the old ones go on for ever.
Ebay would be cheaper.
Also check the head room. Some of the old ones are only 7'ft but it sounds like this is taller. You need 7'6 really for anything over 15.2.
Not sure about the weight but it might be written on it somewhere!! On my old one it was on the hitch.
I dont think you can go wrong with a Rice personally. They are lovely to tow and good sturdy boxes.
ETA When I was looking for my old Rice (I have a bigger one now) I was looking at some boxes that were over 20 years old and still in good order. The twenty year old rices were generally in better shape than other makes that were substantially younger, ie 3 years old!!!