A few years ago I bought a used REL Q108MK2 that's an oldie but goodie...sounds great and has more adjustability than newer RELs. Around 200 bucks.
Inexpensive but decent 8" subwoofers
My current setup is Bluesound Powernode (N330) -> Blueroom Minipods
Which obviously isn't a high end system, but balances decent sound with sleek looks.
Looking for a 8" subwoofer which won't break the bank. Bonus points if it also looks good/minimal!