I own and live in a 4 bedroom house in North Royalton, Ohio which we
built in 1991. I suspect that I may be able to save some money on
heating costs, but I don't have the know-how regarding which
improvements will really pay off. I'm curious as to whether or not an
energy audit is worth the money. Which companies in my area will come
to my home and perform an energy audit, and about how much will it
cost?

It might be nice if the company you will be getting can offer
Performance Contracting - meaning no initial cash layout for the
services. You share the savings earned from the Energy Conservation
projects they recommend for a certain period until the cost of
services and equipment is recovered. In this way, you are guaranteed
that there is indeed savings that can be generated from their service.
What they do is make an initial survey of your house using different
equipment like data logging, thermal scanning, etc. to see what
potential savings can be implemented. They will usually look at your
lights (high or low wattage), HVAC, insulation, pumps if you have,
etc.

But for a residential house, don't expect much reduction in your
electrical bill. Significant savings can usually be seen in commercial
establishments.

Hope I didn't add to your problem :>