The cheapest flights to Quito from San Francisco are still just under $600 (and have been this way for the last year).
Cheap Flights to Quito from San Francisco
The cheapest flights in August leave on August 8th and August 9th. Flights in September and October tend to be the cheapest on Tuesdays and Wednesdays.
In addition to being known as a jump off point before heading to the Galapagos Islands, there is no shortage of sight seeing and adventure tours in greater Quito and the rest of Ecuador.