Just like smartphones, there are literally tons of options out there for expandable storage, but also like smartphones, you may not want to skimp and get the absolute cheapest option. Memory cards, after all, are your backup for all of the important stuff you want to keep stored, like pictures, videos, music, and any files you may need for work or school. When it comes to memory cards, it's hard to find something better than what's offered by SanDisk, but as the quality of their cards are higher, so are the prices. That said, right now you can pick up the SanDisk Ultra 200GB MicroSD card for just $64, which is quite a bit less than it would normally cost.
The SanDisk 200GB MicroSD is a class 10 card, meaning that you will be getting some really fast read and write speeds. This will help to ensure that transfer happen quickly and that the card is able to load content fast when you try to view files. Class 10 also helps for support for Full HD video which is especially handy if you use your smartphone for video recording often enough. In addition to the MicroSD card, you'll also end up getting an SD adapter so that you can use the card for other devices which take the larger size card.