Dave, Yamaha guitars weren't that cheap 35 years ago. I paid £49.00 for my FG160 in 1971, and the average week's wages were around £11.00 - which would make it well over a grand by today's prices!

As I recall, the numbers worked a little differently each year or so - the FG160 was the cheaper one, and the FG200 was the 'posh' version (and I've now got one). The cheaper version of the FG180 was the FG140.