Depends on the surgeon to be fair. While some will insist on very expensive bariatric multivitamins, I've worked with a couple that are fine with Swisse, centrum etc. I suspect it's because they know how expensive bariatric specific vitamins are so would rather their patients took something (even if less desirable) than none at all.
Another fun thing is that cheaper calcium supplements made out of calcium carbonate are off the table because bariatric patients cannot absorb them as easily as the more expensive and harder to find calcium citrate.
Swisse and Costco's Kirkland brand are both calcium citrate. Both cheap to purchase especially Swisse which are more often than not half price in one supermarket chain or another. It's really not that expensive, even when you have to take two doses a day after a malabsorption surgery like gastric bypass. As for iron supplements, many surgeons will steer patients away from them because they complicate calcium absorption, and are rough on the digestive system. These days it's easier just to get an iron infusion when iron levels go too low. Same with B12 that is poorly absorbed after WLS, a three monthly injection is easier and less expensive than oral supplements, plus by injecting they know it goes into the bloodstream and not straight through the bowel. Here it is AUS $9 for three vials which last 9 months.