Inexpensive but decent 8" subwoofers

Thank you all for your suggestions.

So based on the price range and the appearance, I have narrowed it to the following ( in approximate order of price, low to high):

Kanto Sub 8

Jamos S 808

Monolith 8 

Audioengine S8

RSL Speedwoofer 10s MKII

Tzero MKIII

Sonos sub

Any of these that I should specifically avoid? Any of these that punch above their weight in terms of sound quality?

The speakers that I have are supposed to be "quick" and hence I was looking for 8" in the first place.

I've been curious about using multiple subs for years so in the last year I've been buying cheap subs off ebay.  There's a custom install only brand named Episode and I bought two of their 8 inch sealed subs and one sealed 10 inch model.  I paid around $150 each for the 8 inchers including shipping.  At that price they're great.  They're reasonably flat to around 40hz where they drop off pretty quickly.  Since it's a custom install only brand it looks like people don't have any idea how to price them so they can be found at great prices somewhat regularly.  They look a lot like the PSB sub series and if you look at some pics the amps are clearly made by the same company.

PSB SubSeries 350 Powered subwoofer | eBay

Episode ES-SUB-EVO10-450 Powered Subwoofer - Gloss White - Tested | eBay

What is your budget?  How big is your “bank”?  Every suggestion here is great,with varying price points. Are you willing to go used? 

One of mine is the SVS 3000 micro. Small but mighty… enough 

Not sure why you’re disregarding the SVS 3000 Micro given its price, performance, built-in room-correction software, and risk-free 45 day trial including shipping both ways, but best of luck whatever you choose.