alison - I've got a friend who plays flute, and knows a couple flute makers. I e-mailed him your question and this was his reply
"Depending on the quality of craftsmanship and sound, I'd pay between $500 and $900 for such a flute. The keys being only silver plated would keep me from going much, if any, higher. If she can find out the maker and the kind of wood it's made from I might be able to narrow the field a bit. Also, tell her to check out the Lark In The Morning website. I don't think they have used, but she can get an idea of the used price in american dollars. I imagine that Elderly's was sigularly unhelpful in the flute department. I don't recall that they sell a keyed flute.
If she would like to talk to me about it directly, you may give her my number.
If you would like his number, or e-mail address, PM me and I'll send it to you.