Hi Josh.
I don't know who was listing the guitar at $750 but that seems wildly optimistic to me. Did the guitar you saw on eBay actually sell for that price? There is no "book value" for this guitar that I'm aware of since it isn't listed in the Blue Book of Acoustic Guitars. I have no clue what book the seller is referring to.
In general, Italian made flat top acoustics from the 60's-70's sell for between $100 to $400 depending on model, inlays etc. If yours matches the guitar pictured on the Fetish Guitar site it is a pretty basic model.
Here's a fairly plain EKO from the period listed for $95 on eBay. I'm not saying your guitar isn't worth a bit more, but nowhere near $750.