Lucky for you, MicroSD cards appear to be way cheaper than they were a year or two ago.
128GB isn't bad, since most Switch games are rather small in size, exceptions being Breath of the Wild, Ultimate, and Hyrule Warriors. Those appear to be about $20 on Amazon right now.
I got this guy for almost $40 last year, but you can get it for almost half that.
For a little less than double the price, you can double your storage by getting a 256GB, but that's only if you're really serious about getting a lot of games digitally. So if you've got additional money and want to not have to worry about storage for a long time,
get this one.
Avoid the officially licensed Nintendo cards, oddly enough. They're much more overpriced and don't function any better than these ones.