I got VERY lucky with some of the early waves of amiibo. At the time, I was only picking up characters who I liked so out of wave 1, I preordered Mario, DK and Marth from Amazon. They showed up the day the game came out and that was that. I remember reading about how rare Villager and Wii Fit were so I went to Target the next day and they still had a Villager and I grabbed him. Over the Christmas months I would get Fox, Kirby, Samus and Yoshi. I secured preorders for several more which would become uncommon in the following months like Captain Falcon, King Dedede, Shulk, Little Mac and Pit too. Some of the more uncommon ones I came across in stores shortly after release like Ike, Robin, Mega Man and Wario. Honestly, the hardest one to get was Ness for me. I couldn't get a preorder because of the server crash so I had to resort to importing one from a guy who I had bought some games from for $25. In hindsight, I wish I hadn't spent almost double the msrp on an amiibo who years later would flood Toys R Us bargain bins, but I got the Ness like a month before he came out in North America.
I pretty much picked the rest of the set up piecemeal as they became available, spending a good chunk of my Amex rewards on ones I was missing in 2016. Now, I've got the full set so I really only worry about preordering the new coming fighters. I've found that since 2015 or so, as long as I kept up on preorders, I was able to get all of them for msrp. In general, the whole thing was a pain in the arse.