Colorado Trail crewing only costs $60 a week for food; according to my sister, you work 4 days & get a couple days off, but you may have to provide your own tent & other camping gear.; some you can drive to; some they jeep you to; some you backpack in & move camp every day.
coloradotrail.org has all the info on 2013 volunteering & there are many spaces left !
gingerbreadman