We've been stung in the past by not booking the insurance excess in advance and ended up paying an additional 100 euros more on the collection day. From looking at most of the larger companies, very few include this cover by default, but their prices are not the most competitive either. There are several local companies on Corfu and from spending a few minutes checking T&Cs most of them include all insurances and very low on no excess at all. Valantis at corfuexplorecarhire.com is one of them. We've also used Valantis when hiring for a few days in San Steph and they've always offered a good service and would definitely recommend them.
This year we're hiring a car for the full 2 weeks of our holiday and the smallest cars with Valantis are coming out at £171 for the full 2 weeks. As we've booked direct at the Perros (once again, can't wait!!) we'd be paying about £40-£50 each way for taxis and we usually hire a car for a couple of days, so doing it this way means we have our own car available for any smaller trips we want.
I'd definitely recommend these guys and also the driving abroad experience. Take your time, give way to locals and you will have a fantastic experience exploring Corfu, its well worth it.
Good luck.