I agree with your position on that in certain instances — poorer absorption, lower bioavailability ==> just take a bigger dose of the cheap one. But I have run into instances where that didn’t work, because a sufficient dose of the poorly absorbed product led to annoying side effects in the digestive system.
Pulverize the capsule, dissolve in water. That should solve the problem. Also, it may be additives such as magnesium acetate, added for a number or reasons. Find one without that.
Also magnesium sterate could be the problem.