Thanks Crashramp, that makes sense now! I thought I'd seen the other Sinbad a few times - but didn't know if I'd just missed seeing the "Eye of the Tiger" bit each time. Just for fun as you mentioned numbers I checked it out:

Sinbad Eye of The Tiger EM 2 Player - 730 units in 1978;

Sinbad (NOT Eye of the Tiger - diff backglass) EM 4 Player - 950 units in 1978.

Sinbad (NOT Eye of the Tiger) SS 4 Player - 12,950 units in 1978.

I don't know much about the current market but if it's in full working order I personally think $1k is not expensive for this machine - it's the rarest version & has a unique backglass while both 4-players seem to share the same or similar backglass art.