I search for these a number of different ways:
"single hop experiment kit" and then sort low to high- these are the 10# Briess 2 row grains (milled or unmilled), 12oz Great Western Caramel 15, and 6 oz of hops kits. There seem to always be some decent deals (<$18) available. Most kits I've gotten were $14.xx. A good way to experiment with lesser known hops.
"unmilled kit grain" or "milled kit grain"- this adds in some of the other named MoreBeer kits with different recipes. For some reason, at least on my computer, the way the words are entered, you get an easier to scan 3 across listing instead of a single column. And when you sort low to high, it doesn't necessarily do that, so you have to scroll through the entire listing. Amazon does not make it easy to do these searches and I also find that you can find some different kits when searching one way and not another, despite the keywords being in the title, so poking around, you can sometimes discover a kit that did not show up previously.
"extract kit outpost"- These come with 7# of ultralight extract. Search "featured" to avoid getting a ton of different extract only listings. These aren't as commonly discounted as the grain kits, but are a better deal, as the 7# LME alone goes for $23 normal price.
If there is a particular deal you might want more of, let's say it is a super deal like a barleywine for $15, you need to order a quantity greater than 1 right off the bat, because once you order 1, the price jumps up to the regular price.
I've heard that if you have any issue at all with their products, they just give it to you free. And most seem to be FREE RETURNS anyway. Not had any problems at all so far. The MoreBeer milled grain is a bit coarse so I have mashed these for two hours to get 72% efficiency.
Both "homebrewers outlet" and "brewmaster" are MoreBeer stores and there are some well priced items there. I got a D-180 for $8 shipped and I have also gotten some Fawcett malts with essentially free shipping, saves a trip to the store or gets me an item without having to buy enough to qualify for free shipping.
Enjoy the hunt!