Since many 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 january 2018.
SA2000: 1300 usd; 1140 euro
SG2000: 1260 usd; 1570 euro
SF1000: 540 usd; 800 euro
FG150: 225 usd; 270 euro
FG180: 320 usd; 400 euro
FG300: 500 usd; 500 euro
The SA2000 is very stable, SG2000 prices go up in Europe. The FG150 seems to get less polular, but the FG180 and FG300 still are wanted guitars.