SATA expanders seem to have more issues than
concur - stay away from SATA expanders.
you would get with just a HBA. SAS expanders seem to work well for most people, but you can get a pair of HBAs for less than the cost of an expander, at least at the time I was looking. I would just get a pair of 8i HBAs unless you get a really good deal on the 4i.
I'd say less than the cost of a SAS3 expander.
If you are talking SAS2 expanders
the venerable HPE one works well for spinners (and SAS2 SSD's) just make sure to update the firmware. There are limitations - 3Gbps for SATA spinners for example but with spinners IMO that's plenty.
This expander I think is still < $20 or so on the bay.
Yikes Chia inflation hit the old SAS2 expanders too. You might ask in the WTB thread as someone may have one of the OLD HPE expanders and are willing to let it go inexpensively.
If you are doing something unraid, zfs etc. etc. where IT mode is preferred connection method and you are using SATA drives then a single 8i HBA and 2 onboard SATA ports (ideally intel chipset) would likely be fine too.