Ouch! I recently booked SFO-SJU for around $250/pp 1-way for April. In my experience the NYC/STT route is always pricey, but what you are seeing sounds way out of line. You might want to just monitor and wait. For example, Delta is quoting your route for a week day in late April 2021 at $145pp 1-way. The same flight on Saturday is almost double that. We usually buy tickets 4 to 8 weeks out and avoid travelling on Friday-Sun. The downside risk of waiting is that you may not get the flight you want. However, your NYC/STT is a popular route with lots of flights.
Hope that helps.