what year is it?
Being a giant dealer I can tell you that the ocr 3 is a beginner road bike. They were made up to last year. This year they are called the Avail.
New last year was 650.00 msrp US $$. Dont know how that converts.
I would say if it's a newer model then 450.00 american would be the most I would pay for one. And it would need to be in top shape.