You have a Besson New Standard manufactured between 1970 and 1974. I would agree with Dave's estimate of price at around $2,500. I am surprised to see a polished silver finish since these were usually either brass or satin silver. Is the receiver a "medium" or bass trombone shank? If bass trombone, I would suggest that this horn is nearer 1974 than 1970. Generally, these do fairly well on eBay.
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band