I know there are several USB hub dongles that could be used in a similar manner, but what I’m looking for is something that occupies a single USB port and offers 3+ slots for SD and/or microSD cards, letting me browse them all from my computer. Are there any such products? I’m ok with buying off Aliexpress
Yes
The term I searched for was “multi SD card reader” this was the first result.
Is there anything similar under 30 dollars?
Unlikely.
A decent single SD card reader is going to be in the $15-20 range. You want 3+ in a single package. So the price will be around 3x Plus the extra component costs needed to put them in the same package. Plus the general per-unit increase of costs for making a niche product.