Here's one from 2014, $5.50 https://www.yelp.com/biz_photos/taqueria-canc%C3%BAn-san-fra...
Here's one from 2015, $6.99 https://www.yelp.com/biz_photos/taqueria-canc%C3%BAn-san-fra...
Here's one from 2014, $5.50 https://www.yelp.com/biz_photos/taqueria-canc%C3%BAn-san-fra...
Here's one from 2015, $6.99 https://www.yelp.com/biz_photos/taqueria-canc%C3%BAn-san-fra...
$5.50 - dated March 14, 2014: https://www.yelp.com/biz_photos/taqueria-cancun-san-francisc...
$5.50 - dated February 28, 2014: https://www.yelp.com/biz_photos/taqueria-cancun-san-francisc...
Mind, that's a regular burrito and it was one of the cheaper ones in SF. El Farolito was around $6 at the time. La Taqueria started at $8 for people who liked to splurge. El Papolote's yuppie burritos were like $10.
The price at Taqueria Cancun jumped again in 2014 iirc after La Taqueria won best burrito in the US normalized the higher price and got them some press (Taqueria Cancun was in one of the final brackets).