I wouldn't bother buying a big supply of grain, yeast, and hops if you are just starting out. There are SOOOO many varieties of each, and as a beginner I'd really focus on trying lots of different varieties to find out what you like before you start thinking about bulk purchases of anything.
First off, you really can't get all that much for $50-100. That's like 2-5 batches of stuff, and I assume you don't want to make the same 2-5 recipes, so just order what you need.
Seriously, just plan ahead and order grains from a good online supplier or your local home brew shop if it's close. Don't try to build up a grain/yeast/hops supply until you know what you're doing.
You'll learn alot more alot faster if you go for variety over quantity at this point.
Also, don't forget that if you ARE going to start stocking grain, you are going to want to buy and store unmilled grain and you'll need your own mill. Don't know if you factored that in!