I Seem to be ordering things for the robot every other day, so thought I should keep track of this. I haven't included any components I already own like the Raspberry Pi itself, PS3 controller etc. One of the surprising costs that I didn't really think of before was the cost of nuts, bolts and spacers. Having said that I've ordered in bulk, so don't expect to have to order any more for a few years to come.
One large cost was motors. I had no idea when it came to motors when I started this project, so ended up going through a number of iterations playing with different speed and torque ratings. I may be able to sell on the excess motors to recuperate some of the costs.
Update - given up tallying the costs - it all got a bit scary - and most of the stuff I'll be able to reuse on other projects.