Searching on United's website, I found seats departing SAN on Wednesday, October 31 and returning from MIA on Wednesday, November 7, 2018. There are other available fall dates starting in late October through early December. Travel dates in January and February of 2019 can be had for about $10 round-trip. Must depart mid-week to get this price point. No minimum stay required.
Have a look at all our current finds departing San Diego on the (SAN) flight deals page.
Need a place to stay in Miami? We've got a full list of available accommodations on the dates mentioned just for you on Hotelwatchdog.