Most teams seem to go with this LEGO Education set  which clocks in at just around $100 and includes lots of useful elements.  You can see a pictorial inventory of the parts included here or here.
 
If you just need some number of specific parts you can buy them through www.bricklink.com.
 
Many attachments are largely built with more common LEGO pieces like bricks and plates (as opposed to obscure Technic pieces), so the kids can always raid their LEGO bins at home too.
 
Stuart
From: [log in to unmask] href="mailto:[log in to unmask]">Taylor Culman
Sent: Saturday, October 29, 2011 10:43 AM
To: [log in to unmask] href="mailto:[log in to unmask]">[log in to unmask]
Subject: [VADCFLL-L] Supplement Pieces
 
Hello Everyone!

I am currently coaching a team and am very new to all of this. We have a very excited group of kids, and very little funding. We have come to the realiztaion that we are going ot need more pieces to build attachments, and other things, I was wondering if anyone could recommend any supplementary kit pieces for under $100.

Thanks so much!
Taylor Culman
Coach Holmes Hawks

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