Hi KingofOld,
Really inexpensive subs ($100 - $150) aren't subwoofers at all. They're really powered woofers with little output below 40 Hz or a bit lower. They'll help with your M22ti, of course, but don't expect deep bass extension or high output at that price. I would include most of the Japanese-branded "subs" in this category.
Other brands to avoid would include several that have gone through various corporate owners and have been cheapened, such as AR and KLH, once prestigious brand names in the 1960's.
Regards,
