Just for those who have never been and may feel impelled to spend over £100 on taxis, may I just clarify that buses NEVER got from Sidari to Arillas and then Agios Stefanos. It makes no sense at all, especially since they completed the Avliotes bypass. The routes from the airport are either via Arillas (dropping off any St George's people for their mini-bus en route). from Arillas to Agios Stefanos and from there on to Sidari; alternatively, they do Sidari first - the road from Corfu Town to Sidari is much faster than the Arillas route - and then it's ten minutes to Agios Stefanos.
A few years ago I made a long complaint to Thomson (TUI) about the habit of picking up and dropping off from all-inclusive gulags close to Corfu Town, and those are now, according to the coach driver who took us very swiftly via Sidari, done by mini-bus.
If you are not on a package you have little choice but to take a taxi, and you need to factor that into the total cost of the holiday. Taking that into account, I don't think DIY trips are actually cheaper than a package.