Hi Mick, I've looked at Unicircuits prices before, but they seem to be extremely expensive by comparison with other sources. Could I suggest trying Badger Graphics (http://www.badgergraphic.com/) who I have been using for years. Shipping costs notwithstanding, Velvia 4x5 sheets are approx 30% cheaper for example. I haven't compared 35mm materials though.

Best, John.