We can’t really recommend specific hardware - there is a huge range to choose from and many competing manufacturers. I would say, don’t bother with anything under about $30 because it is probably not very good. I use a Behringer UCA 202, which costs around $30 - It is very basic - few features, just stereo line in, stereo line out and headphones out (no input level adjustment, so that has to be done with the keyboard volume control), but I find it works very well. Additional features will generally cost a bit more. We have a few reviews in this topic: https://forum.audacityteam.org/t/sound-card-reviews/8375/1 but note that lists only a very few of the dozens of available devices.