I have had zero luck in waiting until almost Christmas or after Christmas for a sale - the trees I like are always gone, but perhaps I'm too picky. I'm very happy with my costco tree I bought last year. I only have 8' ceilings, so the 7.5' tree is all that would work - but they tend to be a lot cheaper than the 9' trees.
If you go to Hobby Lobby, they take coupons if you pull it up on your phone and almost every week the coupon is for 40% off one regular priced item.