Walmart has Remington Express 00Buck in bulk packs (15 rounds) for $6.47 last time I bought some. It patterns well.
Midway has a decent selection. I really like the Winchester Buckshot. It is buffered and patterns extremely well. Midway is a great company to deal with; I buy from them before I buy from anybody else.
Another good source is
OutdoorMarksman. They seem to have stuff in stock that others don't offer. They are very good to do business with.
I've never tried Wolf so I can't give you an opinion on it.
I don't care for the S&B stuff; it doesn't pattern all that well.
Remington Express is good;
Winchester is better.
I generally use the Remington 00Buck for testing, and load the gun with #1Buck for actual defense work. The #1Buck is a happy inbetween for 00 and #4Buck. The pellets are a good size/weight, and the Winchester variety patterns really well.
Before you buy cases of ammo, consider buying just a few boxes for testing. See what works better, then buy it by the case.