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I would suggest buying now.
If you don’t purchase basic economy tix, most airlines will allow for you to rebook at the lower fare with no fee, and give you a travel credit for the difference.
Of course this plan is only good if you will be able to use the flight credit within 12 months of the original purchase.
Definitely check with your airline of choice and confirm their cancellation policy, but I know this is the case with AA and a few others.
Good luck and have fun