Woot offers SanDisk microSDXC Card, Licensed for Nintendo Switch, 256GB (Bulk Packaging) for $19.99 (orig. $34.99) + free shipping with Prime.

Product Description:
The units in this sale are new condition, unused returns which do not ship in original retail packaging. They will ship in generic bulk packaging.

• Incredible speeds in a microSD card officially licensed for the Nintendo Switch and Nintendo Switch Lite systems (also works with any other device that supports microSDXC)
• Spend less time waiting and more time playing with read speeds up to 100MB/s and write speeds up to 90MB/s.
• Store your downloaded games, screenshots and video captures in 1 place so you can travel light. 
• Nintendo trademarks are properties of Nintendo. 
• Compatible with microSDHC, microSDXC, microSDHC UHS-I, and microSDXC UHS-I supporting host devices