Just as an example without small caps, you might go with:
60% VINIX (S&P 500, 0.035%)
30% VTSNX (int'l, 0.08%)
10% VBTIX (bond, 0.04%)
That gives you an expense ratio of (.6 x VINIX + .3 x VTSNX + .1 x VBTIX) = 0.049%
Slightly better is splitting U.S. into S&P 500 and mid/small cap by replacing about 1/5th of VINIX with VIEIX (mid/small cap).