Since a few years I keep track of vintage Yamaha sellings on ebay. A good way just to get some idea of Yamaha prices.
Below are ebay prices for some of the most sold vintage Yamaha guitars. Prices are average prices sold on ebay with at least 10 sellings per year. The USD price is for US and Japan sells. The Euro price is for EU sellings, mainly ebay UK and Germany.
My experience is that EU prices match US and Japan prices including shipping, tax etc. In many cases buying a certain guitar in Europe directly is about the same total costs as importing from the US of Japan.
Given prices are valid for guitars in original condition, acoustics all red label Nippon Gakki, electrics late 70’ies early 80’ies.
Average prices by december 2014 (I added the difference in % with the 2013 prices).
SA2000: 1290 usd (+ 5%)
SG2000: 1600 usd (+ 40%); 1200 euro (+ 10%)
SF1000: 540 usd (- 20%)
FG150: 285 usd (- 5%)
FG180: 330 usd (- 5%)
FG300: 480 usd (- 25%); 445 euro (+ 5%)
For some vintage Yamaha guitars it’s almost impossible to give a realistic average price. Some only can be found for sale very rare. Guitars like the SG3000, Weddingtons, or the high end FG’s sometimes sell for very high prices.