Wow! She's beautiful... looks almost to clean for an original 1887. Did you happen to ask if any parts had been replaced and/or does it matter to you if it has been restored or not?
I think sewing machines are unique, just as the people who buy them. If you like her and can afford the asking price then all is good. If you are looking for an investment, I think Billy wrote once that sewing machines are a bad investment... unless they are free : ) Maybe someone else can offer better advice on value.
Here's some New Home Info:
http://needlebar.org/nbwiki/index.ph...achine_Company
Again, she looks like a beauty. Good Luck!