approximate price quest

[hkutney]

My husband received as a gift a bottle of Dow's 1977 Silver Jubilee Vintage Porto. The label being bottled in 1979 "produced in the 25th year of the reign of H.M. Queen Elizabth II".
Any idea what the going price is for such a wonderful Vintage?
Also, we are planning on storing it away for about 27 years(for our 50th anniversary). It should only get better, yes?

Thank you.
Heidi