Depends, do you want the signed copy or unsigned copy. The audiobook (which I highly recommend Jeff Hays if FANTASTIC), hardback, or the first two are now available in paperback. If the signed copy look up Invitation Bookshop. They sell the signed copy there directly from Matt for only $20-$30. If audiobooks Amazon is the only place you can get those, for about $27 or less each. The hardbacks are generally around $20 each, while the paperbacks are $12 to $15.
I recommend the hard cover or the audiobook. If you want to read the physical book, this is good enough you'd be happy you got the hard cover, I also love the unhinged quotes under the dust cover XD. But I know nothing of signed copies or special editions at the moment. I second that the audiobook slaps if you do read books through audiobooks
The entire series (8 books) is also available on Kindle Unlimited. There's a very specific book store that sells the signed copies for no aditional cost and I had it noted somewhere but lost it. I'm sure you can find it on the DCC subreddit if you have reddit.
Ah forgot to say that both the audiobooks and the physical books have exclusive extras with both of them. You get the Backstage at the Pineapple Cabaret chapters with the physical books that don’t come with the audiobooks (the hardcovers also have quotes from the books under the dust jackets), while the audiobooks have exclusive things like a song sung by Donut added to them that aren’t available with the physical copies. (The song is freaking awesome btw and currently my ringtone (๑•ㅂ•)و✧ )
THIS HAVE A BOOK!!! OMG HOW MUCH IS IT?