When is the cheapest time to fly from Xinjiang to Xi'an?

This is not very expensive as long as it is not during the Golden Week or the New Year holiday. The following are the recent air ticket prices: ·05-01 Urumqi-Xi'an 487 yuan (24% off) ·05-02 Urumqi-Xi'an 487 yuan (24% off) ·05-03 Urumqi-Xi'an 559 yuan (22% off) ·05-04 Urumqi-Xi'an 500 yuan (25% off) ·05-05 Urumqi-Xi'an 570 yuan (22% off) ·05-06 Urumqi-Xi'an 550 yuan (23% off) ·05-07 Urumqi-Xi'an 544 yuan (23% off) ·05 -08 Urumqi-Xi'an 550 yuan (23% off) ·05-09 Urumqi-Xi'an 500 yuan (25% off) ·05-10 Urumqi-Xi'an 530 yuan (26% off) ·05-11 Urumqi-Xi'an 550 yuan (23% off) ·05-12 Urumqi-Xi'an 550 yuan (23% off) ·05-13 Urumqi-Xi'an 544 yuan (23% off) ·05-14 Urumqi-Xi'an 544 yuan (23% off) ·05-15 Urumqi-Xi'an 539 yuan (2.7% off) Discount) ·05-16 Urumqi-Xi'an 480 yuan (24% off) ·05-17 Urumqi-Xi'an 480 yuan (24% off) ·05-18 Urumqi-Xi'an 480 yuan (24% off)