In some large operations, it can be a team of people. In smaller to mid-sized firms, it can often be someone already juggling other duties, and always does seem to fall with the person already responsible for Quality Assurance (not necessarily a bad thing - they do know production extremely well).
Compared to these costs, the certification service itself is cheap. Whenever companies approach certification for the first time, this is one thing we always warn them about - the money you pay for certification will not be your major expense, but rather, your highest costs will be with staff time.
The other major point to consider is will certification mean your business will be able to grow on to bigger and better things? A GFSI benchmarked certification (usually SQF or BRC) is usually necessary to trade with the major retailers these days, such as Wal-Mart, Costco or any of the local chains. Will the costs of certification (and all the associated indirect costs of peoples time) be outweighed by the value of having a larger market to sell to?
That's not a question we can answer for you, but it is a question we ask our clients all the time - will being certified help you remain competitive, attract new clients, and increase revenue?