Hey there,
It'd be nice to have some more details on hand, so as to give you a real offer and time estimate.
A couple of questions I'd like answered:
* Which shell? sh, bash etc.
* Would I have access to the system in question? If not, that'd be a debug nightmare and I'd probably not take on this project however much you offered.
* What distro do the system have?
* What do the cron job need to do (e.g. rotate logs, send email, process transactions from a database etc.)
Take care, and I hope to hear from you soon,
Marcus