Just found the device I initially wanted to recommend, it is 6 digit though and needs an external battery for retention but at 5uA should last for quite some time!
It is the TRUMETER 7000AS avaliable here for less than £14 +VAT.
http://www.countersales.co.uk/produc...FcMKfAod_0C50Q
The info sheet on it is at:
http://www.countersales.co.uk/datash...SDatasheet.pdf
I have used these as timers in the past, feeding them with a gated stream of 100ms pulses then resetting after a read time before gating again. This was for battery operated equipment. Not used the 7000AS Bi-directional model myself but I am tempted to get one myself for experimenting with.
Les