I would say US $1200 - US $3000

I THINK this may be one but can't see the photo closely enough

http://www.gunsamerica.com/guns/976704137.htm

Some have goo bores, some bad deending on how much they
were shot with old 303 Cases and how well they were cleaned.

Most of the ones I have seen used are very accurate.

500 Nitro