Do you shoot with a Sony a7r II or Sony RX100 IV camera? Both cameras are incredible, but there are very specific SD cards you must use in order to shoot 4K video or high-frame-rate video: UHS-I Class U3 or UHS-II Class U3 SDXC cards.
I happen to own a bunch of Lexar SDHC UHS-II Class U3 cards, which are blazingly fast (1000x and 2000x cards), but neither the a7r II nor the RX100 support 4K/HFR video when using those cards.
Amazon has Lexar 633x 64GB SDXC UHS-I/U3 SD cards for about $27. On Thanksgiving, 64GB cards were on sale for $24, and 128GB cards were $44 (now $57), but they are back up to their normal prices now. 64GB SDXC UHS-II/U3 cards are $35 (1000x speed) and $95 (2000x speed), so there is a significant jump in pricing to go faster. If you do decide to use UHS-II media, you will need a card reader that supports UHS-II. I also haven't personally confirmed that SDXC UHS-II media works in 4K on the a7r II and RX100 IV, but I've read that it works.
In general, I recommend not buying more media than you need because it only gets cheaper and cheaper over time. But in this case, these particular cameras want older, slower media, so I am stocking up because I'm afraid they will start to be made in less quantity, which might drive up prices or make them hard to find. I can always bundle these SD cards with the cameras when I sell them in a couple years, since the cameras will not be able to take advantage of faster media.
If you want to know more, DPReview breaks down the various card specifications and what you can do with them on an RX100 IV.