I've got a few things in my Amazon wishlist that I'd like, but are too expensive right now. The prices tend to fluctuate, and I'd like to buy it once it's below a certain price. Can this be done?
You can sign up at http://camelcamelcamel.com to get email alerts when prices drop at Amazon.
Yes, this can be done.
First, you need to create a way to check the product's price. You could use Amazon's Product Advertising API, or another method (e.g. web scraping with PhantomJS). If this is all you need, you could use prebuilt tools like camelcamelcamel or thetracktor.com.
Next, you need a way to complete the purchase. The Zinc API will allow you to place an order to Amazon on your account using a couple of API calls. Your script could make these calls when the price drops below your threshold to complete the purchase.
DISCLAIMER: Zinc is a tool that I built.