A big bag of grass seed will cost less than a pallet of sod, but that is like comparing the cost of raw wool to a fine sweater. Turfgrass sod is a finished product that will provide nearly instant use, beauty and environmental benefits, whereas seed is an unknown that requires two or more years of on-going time, attention, water, fertilizer and pesticides to reach a maturity equal to sod on its first day.
For more information click to "Self-Scoring Method: How To Establish A Lawn."