Have you looked at the Team Drawings, rather than the Official
FIRST Drawings? They usually give a lower cost version of the field (etc.) that is a good approximation to the real field (etc.)
http://usfirst.org/community/frc/content.aspx?id=11626
Edit: Additionally, perhaps you can talk to local suppliers about your team and see if they'd like to support your team by donating some of the supplies?