Not sure I entirely agree with this. To my understanding, when you are simply observing a horse at the trot, you cannot isolate front end or back end. You need to do flexion tests on a straight away and a circle (and possibly nerve blocks) to figure out precisely where it is at.
From the OP's video, I see the horse's head going UP when the front left and right hind are coming into contact with the ground, which would indicate the problem is in one of those two limbs.
While most problems end up being in the hind end, I don't see how you can say the problem is in the back end. Because the horse will have upward head movement for a front end problem too; it just depends which legs are striking the ground at the trot. Unless you are seeing something I am not.
Do you have a good lameness vet in your area? Honestly, that is where I would spend my money first. Your horse may still need a chiro adjustment (and it's never a bad idea to have them checked), but if you've only got so much money to spend, I'd spend it on the vet.