I'd like to compare our plan's fees with those of other small plans in the $3-5M range
The most effective way to achieve a true benchmark comparison is to ask your advisor to provide a full analysis of their fees as well as the fees levied by your provider. If your advisor is not doing this every few years they should be as they need to assert that their fees are reasonable. I would be happy to provide a no-commitment analysis of your fees and their comparison to plans of similar participant and asset size. Feel free to reach out if your are interested.
You can purchase a database such as the Fee Benchmarker by fi360/Ann Schleck (I recommend you don't), or call service providers around town to get quotes. You can also find other plans of that size and call them and ask what they are paying.