Finding affordable prankster books for kids means getting creative with sources beyond just new retail. My kids love the 'Captain Underpants' and 'Big Nate' series, but buying the latest hardcovers adds up fast. We've had great luck at local library book sales, where they often have entire boxes of used kids' chapter books for a dollar or less. Thrift stores can be hit or miss, but if you go regularly, you'll start finding those worn-out paperbacks with the silly covers. Another idea is checking online used book markets, like AbeBooks or even eBay lots, where you can sometimes buy a whole set of 'Diary of a Wimpy Kid' books for the price of one new. I also keep an eye on digital deals; Amazon often puts the first book in a series like 'Timmy Failure' on sale for Kindle to hook you. The key is to look for series that have been around a while—the novelty books come and go, but the classics are always being resold. It's a bit of a treasure hunt, but half the fun for my kids is the surprise of what we'll find next.
I'd also recommend not sleeping on audiobooks if your kid enjoys listening. Services like Audible sometimes have sales where kids' titles are deeply discounted, and you can find prankster-style stories read by really funny narrators. Libraries are, of course, the ultimate free option—they usually have a robust collection of humor series. Just ask the children's librarian for the 'funny books' section. Sometimes the library will even sell withdrawn copies for next to nothing, which is how we got our hands on a slightly ripped but perfectly readable 'The Terrible Two'.
In the end, the prankster genre is popular enough that used copies are plentiful. You just need to know where to look and be a little patient. My youngest doesn't even care if the cover is a bit bent; he's just happy to get a new story about someone causing chaos.