401K and Retirement Recordkeeper Suppliers

Our finance area has recently engaged our procurement services to assist them in reviewing our 401K and retirement plan recordkeeping supplier contracts, and to consider soliciting RFP's, and/or negotiations.

Knowing little about this category of service, I am trying to locate benchmarks, professional associations that may have a membership for these types of firms, and other procurement professional's I can speak with to better understand the fee structures, etc.

Any help or insight is appreciated.

Thank you.
Debbie