Condition?
Having rego suggests its not a total dog, but obviously an immaculate original one will be worth a heap more than a rough/bodged up dunger that happens to run.
CT1s are a limited appeal bike, and its very rare to see a rego'd one for sale.
The closest example I can think of, is a very good (but not perfect) original-contidition AT1* that went for ~$1000 on Epay a couple of years ago. It was on historic rego (Vic or NSW, I can't remember which), and had a GYT pipe.
On the other end of the spectrum, crappy runners seem to struggle to fetch $250.
Also, the early ones with the piston port motors are marginally more desirable than the later reed valve models.
*The AT1 is the 125cc version of the CT1. Basically, the AT1 is the bike they made before they started making DT125s, and your CT1 is the bike they made before they started making DT175s.