We talked about this in Discord but I thought more people should know about it.
TLDR: sign up at Is There Any Deal?, add games you want to buy, and specify the target price. You can use a price filter (eg. under $30), and/or a percent filter (eg. 70% off).
And then, apply a liberal dose of patience. If you can wait it out, you’ll get an email when your items go on sale with the price-points you specified. They also email you the historical lowest price, so you can compare and decide if you want to wait more or just buy it.
Overall, highly recommended for those who are okay buying on Steam, and/or patient enough to wait it out.