Storage is insanely cheap these days by any traditional standard, and the same will probably be true in the future. Still, it's especially cheap today in particular thanks to Amazon's Goldbox deal. Kingston flash memory is discounted by as much as 65% off list price, and that includes microSD cards that can be plugged into your devices.
If you just need a simple USB 3.0 flash drive, take a look at the Data Traveler 3.0 – the 32GB is only $12.99 today, or you could go all the way up to 128GB for $56.99. You just need an OTG cable to use them on most devices. Probably of most interest are the deals on microSD cards, which are ready for insertion into any number of Android devices. There is a 16GB card for $7.99, 32GB for $15.99, and a 64GB card for $34.99. Those are darn good deals. There are also regular SD cards, but that's not much good for Android.
It looks like all the Kingston flash products are Amazon Prime, so shipping shouldn't be an issue. Just remember, the deals are good today only.