You can find flights at this price starting in late August through March of 2019. However, dates in December and January seemed to be blacked-out. Travel is available daily, but you'll have the best luck departing midweek during some travel windows. There is no minimum stay required.
Searching on Copa's website, I found seats departing LAX on Wednesday, October 10, and returning from POS on Sunday, October 14, 2018.
If you're in the market for a different destination, here's a full list of deals from Los Angeles (LAX) that we've found today.
Need a place by the beach? We've got you sorted with a few available accommodations for the listed dates above on Hotelwatchdog.