I have an Adam Audio Sub-12 for my entertainment system but wanted a cheaper smaller subwoofer for the office where I spend most of my day working, playing games, and even watching some HBO Now. I found some
sub recommendations here for quite a few options. I couldn't justify dropping another two grand on a sub (I was pleased to see they recommend the Sub-8 though).
Their budget pick was the KRK K10S. I was skeptical to buy a less-than-$300 sub that had a 10 inch woofer but the specs said it could hit down to 34 Hz, which is good enough for my near-field listening in that tiny room. I've enjoyed it and think you would too, if you can stomach the yellow cone. It's under my desk so I don't even see it, but it was a turn off.