According to the airline, you can book
Aeromexico last-minute deals at midnight or in the early morning when very few bookings happen; because of this, the booking window gets free for users, so you have the chance to grab the best deal according to your budget.
You can also get the cheapest flight ticket if you book your flight in advance, between four months and three weeks prior to the flight departure date. Instead of that, if you get closer to the flight departure schedule, then it may be possible you will get an expensive flight ticket.
You can also try during the off-season,
mid-April to mid-June, and September to mid, November when the ticket price gets reduced because people do not prefer to travel during these time durations, so the demand for flight ticket get reduced in order to increase flight ticket sale airline reduce the price so that can be suitable for you to book a flight ticket at affordable price.
You can also get the cheapest flight ticket through vouchers and coupons, which will reduce the price and make it affordable for you.
For further information, you can get through this article and clear your doubts.