Why the focus on small 401(k) plans? Because costs are less of an issue with large plans. At the far extreme of low cost, the government's Thrift Savings Plan has annual costs, all in, of 3 basis points. [...] when it comes to small plans, the cost can be determined as much by whom the boss plays golf with as by the seeking of the best return on the employee benefit buck. In a recent telephone interview, Joseph Valletta, co-publisher of the book, said "employers usually have the highest balances in the plans, so they have a vested interest in keeping plan costs low." Of that amount, 1.38 percent goes to investment expenses (the expenses of the underlying mutual funds), 0.13 percent for record-keeping administration and 0.02 percent for trustee fees. [...] a map is available - "The 401(k) Averages Book." [...] the problem of high expenses diminishes as plans grow larger.