Expensive for the quality, but the quantity is relatively high.
As one of only two (I think) places in York serving Mexican food, Fiesta enjoys a lack of competition, and does not really offer anything very special. The staff is friendly, but the place does get very busy and is popular with young people. It also caters for parties, so do not expect prompt service. However, the food is fresh, and they will cater to people with allergies and special dietary requirements.