This sounds like a really fun challenge.
Head to the thrift store. There are PLENTY of fleeces, running shorts, synthetic shirts, hats, old running shoes, etc. to go around. Bonus points for awesome colors.
I have a 600-fill down jacket that weighs 18 oz and cost me $.50 at Salvation Army. Seriously.
Driduck/Frogg Toggs sounds like a good bet too since a rain jacket might be hard to find used.
$200 almost sounds like too much if you go all used.
There are so many perfectly good clothes in this world, don't go to Walmart. (Ok, maybe for undies - which are more like $8 for 100% synthetic.)