Arne Jacobsen butterfly chairs  

Butterfly
Which is the butterfly chair? Do you mean the 3107 (Series 7)?
What is the age and what type of wood veneer?

Some rules to respect
3. Identification requests are welcome under the condition that the object corresponds to the general topic of the website (no antiques). These request may concern identification of designers, producers, periods, styles or materials etc. but not their commercial value. This forum is not a free valuation service!
These are posted at the top of the forum page.

You can easily see how much t...
You can easily see how much they are worth by searching ebay and google for auctions.
Asking here really doesn't make sense, as we are an international forum and worth is depending much on locale.

Sounds like
Sounds like the Series 7 chair (1st picture below, right)
Or could be the Ant (1st picture, left) or Grand Prix (2nd) or 3103 (3rd)
There are a few other lesser known chairs in the plywood series.
Value, as has been pointed out, is what someone is willing to pay in their geographic region. In Northeast US - maybe $100 - $300 / chair depending on what sort of condition & wood type they're in.