I would call Bariatric Advantage (800.898.6888 ) and Celebrate Vitamins (877) 424-1953) and ask them about programs or options --- before I would even look at finding the cheapest possible thing. You do NOT want childrens' chewables - period. Centrum ADULT makes a chewable that is good if you can't swallow pills.
Read this (http://wlsvitagarten.com/
) if you're unsure what vitamin deficiencies can do --- Make sure you are getting your labs and taking what you need BEFORE you end up wtih problems. When you signed up for surgery, hopefully they made you well aware you were also signing up for a lifetime of vitamins.
I don't know how far out you are, but after awhile, you can probably eat enough protein -- if you fill your diet with GOOD greek yogurt (not the ones that call themselves greek yogurt but have 20g sugar), cottage cheese, seafood, fish, chicken etc...
The person who mentioned Body Fortress is right -- at least it is mostly whey protein isolate, very cheap and tastes pretty good. EAS probably not a good choice as most of them have very little whey protein isolate. Muscle Milk is extremely high in calories unless you look at MM Light. Atkins is not good, no whey protein at all and very little protein total anyway. You can customize your protein at http://trueprotein.com
and buy in smaller quantities so its preyty cheap -- just an option.
Here is another idea: for your birthday, christmas, whatever --- give your family/friends links to thinks you need. Last year I got 90 days of vitamins from my parents and 2 big jugs of GOOD protein from my sister.