I used owners.com (bought the sign at home depot, which came with a free listing). They mailed me a sticker to put on the sign w/my phone number, website link. Also used this link for newspaper listing. This in SLC area in Utah. Since it was a sellers market then, I didn’t see the need to list on the MLS. About half the phone calls I got were from realtors, anyway.
I would probably have a different strategy depending on RE market conditions in your area. At the time I sold, Utah was pretty active. Looks like it’s slowing down a bit (saw this coming, was why I sold). This was the second property I sold FSBO (nope, not an specuvestor) so I was comfortable with the process. Good luck!