How to select a subwoofer

My current system is shaping up nicely. My next step is to decide on a sub to obtain deeper and tighter bass. My speakers go to 25hz and my room is 14wx22lx9high. I enjoy classical with other genre. The issue of budget is always a question and it should be below 3,0000. Different companies have various setups so I would like suggestions that you enjoy. Thanks, Steve