Sometimes the best gift you can give to someone is to accept their generosity gracefully. Giving in that amount makes them happy for whatever reason, so just go with it. It's perfectly fine for you to keep your gifts to them to what you can afford.
If they were bothered by the inequity, they would scale back with you. So believe them when they say that they want to do it.
I agree with this.
And I absolutely agree that the bond is the point--it is, in fact, the ONLY purpose of presents, to deepen the relationship
between the two parties.
I have found over the years that some of the best presents were inexpensive but perfectly picked (yes, even regifting--once I snagged a pitcher from the test-kitchen giveaway shelf because it was the duplicate of one my mom had lovedlovedloved and broken--best gift ever, and sort of more special because it came in such a quirky way).
And I've discovered as well that "who gets the expensive gift" would shift from year to year. One year Mom, the next year DBro2, the next year DSis, the next year Mom, the next year Dad...
But I can totally understand your discomfort with it. And I do think that while the gift is the giver's choice, it can be really, really rude to give a too-generous present.
If you find that the disparity is REALLY bothering you, then I think you are totally within etiquette to explain to these friends that this disparity is interfering with your friendship, and that the friendship is too important to risk in this way. And then ask them to either scale back a bit, or suggest that you only exchange edibles (in which homemade is often far better, so you
win), or suggest that you skip presents since you're all grownups.
(And if you ever need to give their kids a present, remember this: A huge, huge box is far more valuable to a little kid than any plastic toy of any sort. And that snagging one from when your landlord replaced the refrigerator is completely kosher.)