One of my projects from last summer was an attempt at a foamy scratch building with a Fan Trainer EDF built from Dollar Tree foam board. I patterned it after the 150% scaled up version of the plans found in this build thread: http://www.rcgroups.com/forums/showthread.php?t=426281.
This was my first attempt at both EDF and at building with foam. The building process went well and I kind of enjoyed working with foam.
The total investment in foam was about $5 (including scrap and re-work). I powered it with a Detrum 70mm Fan combo from HobbyPartz.com which includes the fan, motor, ESC, and servos for under $50. All in, with batteries, and a 4 channel receiver, total investment was under $100.
Unfortunately, it did not survive its maiden flight. The wings were simply not stiff enough and fluttered badly. Apply enough power to keep the plane flying, and the wings flapped like a hummingbird. Back off the power, and there was virtually no control. I ended up lawn-darting and disintegrating everything from the wings forward (sorry, no picture of the damage).
Oh well, nothing ventured nothing gained. The electronics and fan escaped unscathed, so the total loss was under $10 (and a little bit of pride). I have a few ideas for how to use the fan and other bits from this attempt in a new creation!