We used the local tour bus of Cagliari which was significantly cheaper than the cruise tour and we visited pretty much the same places.

It was a super open air bus which took us all over - we saw the beach, the historic and newer towns, building of interest etc.

It was a great tour and around 10 euros (2007 if memory serves - I know we were impressed and thought it great value for money)

The bus was clean and comfortable with a lovely guide who explained everything to us.

Well worth it - it picks up from most places but your best (at least in 2007) not to pick it up at the 'front' as there will be queues.  We were told to pick it up just up the hillside.

At the time there was a small tourist booth that gave us the info - with your back to the sea, cross the road and it was over to the left (just watch the traffic!!!)

I cant say what the prices are like now or even if it runs, but it was a great day out for more than half the cost of the cruise tour and well worth it to see as much as we did.