While it seems cold and unspiritual to put a price tag on faith, it is educational when someone attempts to.  Over at the Evangelism Today Blog they have referenced an interesting number.

$ cost per baptism (or why we believe in sending money to the mission field): in USA, $1,551,466; in Mozambique, $1,366; in India, $9,803. (World Christian Encyclopedia)

Source: http://evangelismtoday.blogspot.com/2006/08/tuesday-morning-evangelistic-smack_22.html