If it’s not frowned upon and you have more teams than you’re ordering field kits for I’d love to buy one of your extras. It won’t end up on Craigslist or Ebay. The mats make for good sensor practice and I don’t think you can ever have too many Technic pieces.
The same is true of any previous extra kits your teams might have if you’re looking to make room and some money.
As a quick aside, on the topic of practice mats, fairly regularly Staples has printing deals including vinyl banners from 3’x1.6’ to 8’x2.5’. They’re not exact field dimensions but we ordered a few for swim team, 6’ x 2.5’ for $20 and had 3 colors. All sorts of challenges you could probably print up for practice missions and programming challenges. Robot^2 has a great set of tiles described in this post: http://robotsquare.com/2012/11/28/line-following/
 with a PDF you can download. I either read on their blog or the RoboCup Jr  Rescue
 that the printed tiles could be mounted on 12x12 vinyl flooring tiles for quick mix and match maps.
By the way, the rabbit hole just gets deeper and deeper, the RobotCup Jr Rescue looks like a great offseason challenge for FLL. If you scroll to the bottom of the Rescue
 page you’ll see a download for the rules that includes tiles (though I’m not sure those in the rules are suitable for printing).