Another way to look at it, realistic Bass is difficult to reproduce. There is a minimum entry fee to get to bass that isn't colored, mushy or just one-note thudding, and that threshold doesn't occur in my opinion until around $500 to $800. Above that you are going to get greater portions of the lower octaves with each exponential increasing increment of investment. It is a matter of physics, low frequency sounds require big drivers, solid boxes and a lot of power to start and stop the big driver. Conversely, bad bass is hard to hide, "thud thud thud".
On the other hand, listenable speakers with reasonably musical midrange can be had for as little as $250 to $300 (see entry level speakers from manufacturers like PSB and Pardigm). These speakers don't display the last word in treble or bass extension, but will get your feet tapping never the less.
So what should you do? If good bass is important to you and your budget is limited, you may want to invest as much or more in your sub as in your speakers (go with monitors). If you have about $3000 to spend on speakers and a sub, you could get some really nice monitors or floor standing speakers for about two grand, and get a nice REL sub for about one grand and have a good time.
There is no hard and fast rule about this, but I think you are guaranteed to be disappointed with a "bargain" subwoofer, no matter what speakers you use.
