Katie, years ago when hubby and I married, we bought for everyone, but very inexpensive gifts. As the years went by and more of us married and then came children, forget it! My family stopped. Hubby's family continued for years and every Christmas we had to go through the humiliation of being handed gifts and not giving any. Finally they started drawing names, we don't go along, they spend more than we can afford.
If you can't afford it, I say like others have mentioned, let it be known and hold your head up high and simply say thank you when given a gift. If others want to continue, so be it. To me Christmas is about so much more than just gifts.