Good budget sub for music?

I agree with the poster who said that your request is an Oxymoron. The qualities of a good sub that makes it capable of integrating seamlessly into a music only system are qualities that do not come cheaply. Adding a sub and intergrating a sub are two different things. Finding a sub that blends with your main speakers without drawing attention to itself is difficult to find...even for subs beyond your budget. I also agree with the poster who recommended the REL Storm III. I use that sub in a 2 channel system and have had success blending it with two separate sets of speakers. The REL Strata would also be one to consider. You might be able to find a used one closer to your budget. A subwoofer not only interacts with the main speakers but also interacts with your room in some pretty significant and sometime unpredictable ways. For this reason I would stongly recommend auditioning them in your home before making a purchase. Good Luck.