You might be interested in a Summary Report where you only have one line for each expense category, the individual transactions would be omitted. This can be done by setting up the summary report you have already described, but on a layout with the body layout part removed.
But to suggest an approach that produces a result more exactly like what you have requested, see this thread on using the ExecuteSQL() function (not the script step) to produce a "summary recap" which could be located at the beginning or end of a report: FMP 12 Tip: Summary Recaps (Portal Subtotals)
Thanks, Phil. I wasn't clever enough too figure out option #2 but I did manage to do option #1 which isn't as ideal but it's certainly better than nothing! Thank-you again for sharing your expertise!