Hey Profiler --
Much like your current situation, I definitely did my very first DragonCon on the quick and dirty -- and relatively cheap too.
Here's the cardboard smartgunner chestplate I did (which Outcry27 referenced above) for a quick and cheap smartgunner outfit in 2005:
It originally started out as the dry-run template from which I was going to build my sheet aluminum one from -- but I ran out of time and was forced to actually build the template and paint it to wear.
Here's my "poor man's" smartgunner load out...
All in all everything took about 7 days to build -- mostly due to the smartgun. Rather plain, but good enough to hang with the boys! I didn't even have a correct set of BDU pants. You can just barely see my $7.99 off-the-shelf headset and thriftstore shoulder lamp build-up in the above photo. I think the freehand smartgun alone was more than a sufficient attention grabber.
Before:
After:
And here's what I used for the shoulder lamp...
...and the final product:
I had purchased nearly everything needed to build the Steadicam arm assembly... but again, ran out of time. If I had started a week earlier it would have definitely been done in time.
And contrary to Rex's flattering embellishment of my aluminum armour build in 2006, it took about 2 days (not 4 hours) from start to finish once I had all the materials:
Start...
...to finish:
That build wasn't entirely cheap though. I'm thinking it cost between $100 and $150 in materials including all of the webbing, helmet, resin/fiberglass bits, and misc.
You have almost exactly a month before DragonCon, you have plenty of time as long as you begin your material shopping now and finish within a week or so.
I personally cheated a little this year for DragonCon and picked up a full set of fiberglass armour -- but it needs a complete build and paint job. Thankfully I already have everything else I need to complete it.
The Dropship pilot would definitely be another great alternative, with really only the helmet being the wildcard. I've seen them sell on eBay with extreme regularity for as cheap as $90, but I also happen to have a somewhat local military surplus store that has sold them in the past for $125. Military jumpsuits are easy to find, and usually run about $30.
I still love Joe's "just woke up from Hypersleep" look -- and hella cheap too!
