How much is appropriate?

My boyfriend’s brother and his fiancée are expecting and there’s a shower for her very soon. Unfortunately I won’t be attending due to some personal circumstances but would like to send something. It’s monetary gift only, but I can’t figure out what’s would be considered an appropriate amount if it’s just from myself. I had initially thought $50 - especially given that I’m not working at the moment - but also don’t want to come across as a cheap or stingy.

Thoughts?

Thanks 🙏

ETA my initial thought around how much to put into a card.