MicroSD cards are nice. They take a tiny amount of internal memory and supplement it with however much space you need to store whatever you want. And those little plastic squares happen to go on sale all the time.
Today you can get Sony flash memory on Amazon for super cheap. A 64GB microSD card will only cost you $18. The larger 128GB option is going for just $43. It's already sold out, but Amazon will still let you place an order, and it will mail one off once it's ready. Just make sure you're buying from the right seller. Otherwise you're looking at spending around $80.
There are other things on sale you can store stuff on as well. Full-sized SD cards are going for around the same price as their micro counterparts. There are also a few flash drives to choose while you're browsing the link below. The sale will end in a little over ten hours.