A really late carb model (old shape) is often worth more than an early injection model. The last of the carb models had all the good bits on (stainless hoses, underslung back brake, carb heaters, etc) and most people prefer the shape. Add a single seat and high lift pipes and you're in SL land which is all good!
If the bike you're looking at is in the uk then it should be worth about £2k - £2.4k depending on when it was last serviced. If it's over £3k then walk away (that's 748/916 territory).
Cheers,
Ali