Find out how much competitive services in your area charge. Generally, consulting firms and independant contractors have very different fee schedules, so that would have a huge impact on where to look.
Your level of experience, expertise, and ability to get the work done quickly likewise should have a tremendous impact on your rates.
Consulting firms in the Chicagoland area tend to charge $100-$250 an hour, depending on the task (desktop support, network administration, network design and project management, etc.) time of day (most charge more for after-hours and weekend work) and person (senior people charging more than junior people).
In comparison, contractors tend to charge somewhat less, from $50-$200/hour, with inexperienced coders charging closer to $50/hr and expert network engineers closer to the higher end of the range.
Hope this is helpful. Post more details about where you work and your level of experience and I might be able to offer more concrete guidelines.