Amazon currently has Samsung's 64GB EVO Select Micro SD Card available for just $19.99. This is a great price for this micro SD card, seeing as it would normally go for around $40-$50. And it's a great way to add some more space to your smartphone's storage.
This micro SD card from Samsung is part of its EVO Select lineup, which will provide you with read speeds of up to 100MB/s and write speeds of up to 60MB/s. That is plenty fast for recording 4K content - something that most smartphones are capable of doing these days. And it is also fast enough for storing apps and games on the micro SD card instead of the internal storage. With this being a 64GB card, you're going to get about 58GB of usable storage. There are a ton of smartphones available on the market right now that support micro SD card slots, including the Galaxy S8, LG V30, and many others. Finally, Samsung does sell this micro SD card with a regular SD card adapter, so it can also be used in a DSLR or another device that uses the full-sized SD cards.
This item is also eligible for Amazon Prime's free shipping. Which includes free two-day shipping, and pretty cheap (usually $3.99) next-day shipping if you need it extra fast. If you are not an Amazon Prime member yet, you can sign up for a free trial of Amazon Prime. You'll get 30 days free (if you're a student, you get 6 months), and then it's $99/year (or $49/year for students). Prime members do get a whole lot more than just free shipping though, so be sure to check out the full benefits.