The Samsung EVO Select MicroSD with 512 GB of storage can now be bought for just $25 on Amazon and Samsung's website. It has read/write speeds of up to 130 MB/s and can work with a variety of devices such as smartphones, tablets and handheld gaming consoles. https://www.notebookcheck.net/Samsung-EVO-Select-MicroSD-card-512-GB-variant-gets-attractive-price-cut.810208.0.html
Be careful, I just bought one of these on Amazon last week and tried to set it up in a new tablet yesterday. It is a fake, would only format as 7.06GB. I checked and the one I ordered was shipped and sold by Amazon.