Saving money on tour is not a concern of mine and I don't track expenses.
But, one way to save money on a bike tour is to use hospitality sites to get places to stay for free. The sites I've used are
www.couchsurfing.com,
www.hospitalityclub.net, and
www.warmshowers.org.
In addition, this page has
2 links to discussions at crazyguyonabike.com about touring costs.
This page is a discussion about the costs of a two-year round-the-world trip:
http://www.mark-ju.net/juliette/planning.htm
Good luck,
Ray