$1 Silver Cert Autographed By Sinatra/Romero

There is a fellow near me that has some silver certs
for sale. I have been in contact with him and it turns
out they are all common dates, HOWEVER, like the title
says, one has been autographed by Frank Sinatra and
Caesar Romero.

The person is asking me to make an offer on the notes, but
to be fair, I suggested he stop by here and see what you
good folks thought the value of a note like that would be.

I'd feel funny just offering an arbitrary amount, and the
thing might actually be worth more than I could afford.
That wouldn't be hard, if you know what I mean!

Maybe he'll stop by and show it off.

Thoughts?
Opinions?
Attempts at valuation?

Thanks!
Dave