Really? In my experience this makes no difference. Alcohol is alcohol inside the body. Its all poison in excess. I have noticed that some of the cheaper beers make for slightly worse headaches, but I think that's just because you drink more beer when its cheap.
Mixing different types of booze worsening a hangover is also a myth.
Where can I buy a saline IV setup...?
Yes, it is controversial, but I believe there is a big difference between boozes. People point to cogeners or fusel oils as possible causes. I don't know the reason, but I can feel it, even with moderate amounts with certain ones. For instance, I like the flavor of both my (Czech) Fernet, and Cynar (artichoke based), but it will take me forever and a half to finish them because they make me feel a bit too funky the next day. Even with modest amounts. Don't get me wrong, you are right in that it's the alcohol that is the greatest culprit.
Going cheap with tequila has a greater repercussion that it might do with others. If it does not say 100% agave right on the bottle itself, then it only requires a minimum of 51% agave! The other 49% can basically be any mystery booze. It does make me wonder if this is partially the reason for why so many people call tequila as "to-kill-ya". There are better "mixtos" out there, but they for sure won't be the cheaper ones.
The French Pastis or Ricard are infamous for being able to give you the worst hangover, evah! They (the French) also believe finer wines are much easier on you the next day.
I recently developed a sweet tooth for Belgian tripels, man oh man oh man oh man, but damn my wallet got light real fast, and I've stayed away from the package store for a while.
I have a weird hypothesis about my favorite cheaper beer of the past, Bud Light. I'm guessing (totally out of my butt) that it is of a higher glycemic index, even though it's not all that high in calories, because I swear that stuff immediately goes to the waistline. I've been on a kick with using russet potatoes every which way, but I'm easing down on those for a similar reason.
For hangovers, I like certain Asian foods, particularly soups, typically of a spicy variety but not always, usually Korean, but also Vietnamese, Japanese, Chinese, maybe Thai. Then watch some movies on the HT.