Obviously something is worth what someone else is willing to pay for it. As a guitar player with 40 years experience I rate these guitar highly, they are not a Martin, Levin, Gibson or Goya standard but on the other hand for £100 – £200 they are a really good sounding guitar, nice narrow neck and light enough to carry around. I am currently selling one and would not accept less than £200 for it.

There’s one being sold on ebay right now with a similar sounding condition.

The current bid is at $20 but it still has 6 days to go – watch the auction and you should get some idea of the value – http://www.ebay.com/itm/Yamaha-FG-420-Acoustic-Guitar-with-Case-D202-/150750371087?pt=Guitar&hash=item23196c1d0f#ht_1387wt_1257

Keep in mind that the auction includes a case.

I’m not in expert in appraisals, but I couldn’t see it being worth more than high end hundreds.