Michelle Murrain has written a wonderful piece at Idealware on the true costs of free and low cost software. Michelle points out:

"When shopping for software, it's important to consider not just the
purchase cost, but the full costs of using that application over time.
While some low-cost software is actually a good deal, other low-cost
packages can be a nightmare of setup woes, training costs, and
processes that just don't fit your organization. In this article, we'll
take a look at all of the costs that might be associated with a piece
of software — both in terms of money and staff time — and the questions
to ask to ensure that an affordable software package is a great deal,
not a lemon."

http://www.idealware.org/articles/true_costs_software.php