We use Pub Kegs, http://pubkeg.com/
Around 30 for the whole thing and around 10 for just the blader. Very light weight so freight won't kill you. We generally use them for retail customers so if they never come back the 30 for a deposit pays for total cost of the unit. I wash the bladder 3 times then toss. Could probably do it a few more times. Completely recyclable, they are like a 5 gallon soda bottle. It doesn't take a lot of time to clean them because you can see inside and how clean they are getting, I can clean and sanitize them in less than a minute. Only pain is cleaning the outside bucket when they come back.
If those cost 100 for the outside I would spend the extra 30 bucks for stainless and not worry about buying bags at 4 bucks a pop.