Without further information on items such as plan design and services the range of potential fees is too broad to provide a meaningful answer. A review of your plan is probably your best approach to establish a benchmark for comparison purposes.
This a great start to you holding up your fiduciary duty to your plan. If the plan has been in place for some time, now is the time to start the RFP process. (Request for proposal) The regular completion of an RFP process (as often as every three to five years) is an essential component of the due diligence process. The reasons include, but are not limited to, the following: Fees per service level, Benchmarking fees, Plan size and Plan participation. The 401k industry is always evolving and your plan may have outgrown your current providers.
It is difficult to give concrete answers without having more information about your particular plan. A plan I just helped switch over to Vanguard was paying around $3300 in TPA fees prior to conversion and they were similar in size to your plan.
As mentioned, there could be other factors, but you can generally get set up with a reputable TPA where TPA and recordkeeping would have a base fee of about $2500 per year and a per-participant fee of about $70 ($2660 for 38 participants), for a total of about $5160, but keep in mind that some companies have arrangements with the mutual funds to pay some costs from the funds instead of directly, often at much higher costs. They might boast very low costs only to charge it as a percentage "kickback" or revenue sharing from the mutual fund or annuity product used as the investment vehicle. Having a ultra clear picture of all costs of your plan, including the advisor fees, the fund costs such as 12b1 fees, commissions and internal operating expenses is vital in comparing the true costs of various options.
You have a nice size plan in terms of assets and with only 38 participants, you have a healthy avg account balance. The cost for record keeping fees is widely disbursed among providers mainly due to the level of services provided. I would suggest having a qualified adviser review your plan and then get proposals from several reputable providers and compare plans. With your plan, I would expect from a provider would be excellent service, sound advice, a full suite of high quality investments and the best value for the price you're paying.