If its a 73 Sedan, it should be a 2 door KE20. 4 Door KE20's weren't delivered in Australia, and I've only ever seen one. If it's a 4 door, it's a collectors item in Oz.
2 door coupe's are KE25's.
A good straight one can be worth anywhere between $600 and $2500. Usuallt around the $1000 and $1200. Would need photos.
Cheers
R