I have just come home from a trip to Melbourne and did the one day Great Ocean Road tour with a company called "A tour with a difference". It was a great day out, starting at 7.15 from my accommodation and returning about 9 pm.
It is a family company with a Mercedes small bus with comfortable seats and only takes 9 people per tour. It included morning tea, lunch at a hotel and light evening meal in a cafe overlooking the water at Port Campbell. They take only small groups and I found that everyone joined in and bonded very quickly - like a big family. The two tour guides (Grace and James) were friendly and knowledgeable, took us to all the sights and because the Gibson Steps were closed for repairs, they even took us to an extra attraction (which had an entry fee) at no extra cost to the guests.
They also do a tour into the Yarra Valley.
The cost of the tour seems to me to be less than most other companies, especially when you take into account that meals are provided. They have a website www.atwad.com.au