Are there any bike computers that give you a five-digit odometer for pure cyclists like myself? If ever, I would pay up to around $25 so as to save money.
Do you have a smartphone? Look for the Strava app which uses http://strava.com/ as a backend to record all your rides.
The number of digits thing becomes irrelevant, and logs which bike did the distance.
You don't need to enter into the competitive side of strava. You can simply make all your rides private by default, and default to viewing your own times instead of the fastest.