As the total solar eclipse on Aug. 21 approaches, people are either trying to catch the event or cash in on it. Tourists are flocking to the path of totality, where the sun will be completely covered by the moon. Hotels are booked. Heck, even Waffle Houses will be packing ’em in for some eggs, sunny-side-down of course.

And perhaps no companies are making more money off the event than those selling solar eclipse glasses, from Amazon to Walmart. If you want a peek at the once-in-a-lifetime solar event, you better have a pair of these shades—or you may go blind, experts warn.

As we’ve gotten closer to the big black out, Amazon’s protective eyewear listings have offered quite the lesson in supply and demand. Listed in various categories throughout the site, the e-commerce giant has many best-selling listings for solar eclipse glasses, and currently, the prices are staggering. How Amazon calculates its best-selling listings isn’t exactly clear, but the company does update its charts hourly.

Using free price tracking tools CamelCamelCamel and TheTracktor, Fortune examined three best-selling solar eclipse glasses listings still available on Amazon, to see how their prices have climbed over the past 90 days.

The first set of best-selling solar eclipse glasses are made by Soluna, and come in 10-packs that are certified to be safe by the International Organization for Standardization, or ISO, and European Commission, or CE. Listed in multiple categories, such as home improvement and camera and photo, the glasses are sold by a third-party seller (not Amazon), and cost $11 on May 17. On July 31, glasses were listed at their lowest price of just $3.69. But since then the price has shot to the moon, climbing more than 4,200% to its current price of $159. (During the time it took to write this article alone, the cost climbed an additional $10.)

The current best-selling glasses in the tools and home improvement category is a five pack of ISO and CE-certified Lunt solar eclipse glasses. On May 17, the glasses cost $8.50. On July 25, the five-pack reached its lowest price, $6.50. Today its priced at $59.95—its highest to date. From lowest to highest cost, the listing has seen an 822% price increase in less than a month.

The last best-seller tops the industrial and scientific category. This four-pack of premium ISO and CE certified Lunt Solar kid-size eclipse viewing glasses cost around $9 on June 28 (the earliest date that CamelCamelCamel could find price information). On July 13, the four-pack dropped to $7.49, and today it climbed to its all-time high $44.95. Compared to the other two listings it’s a steal, but the price of the still climbed 500%.

If you haven’t bought any yet, you may think you can go without. Think again. Even looking up for just a few seconds can cause eclipse blindness. And then you’ll wish you had overpaid for some glasses.