Maybe it's my imagination, but we seem to be living in the golden age of subwoofers. IMHO, the economics of high end loudspeakers are really being transformed by these developments.
I agree things are getting incredibly cheap now that most everything is made in China but I am not sure that the sound is all that good on these cheap subs. The physics of LF sound reproduction determines that a good subwoofer that has meaningful output at 20 Hz, a good transient response and less than 1% harmonic distortion will remain large and rather expensive compared to a regular speaker that lacks LF extension.