Please suggest bookshelf with best bass response under $4000 pr.

The laws of physics remain what they are. You cannot get deep bass out of a small box and small drivers. The more you push low frequency extension, the higher the distortion. Of course technology marches on, but only slowly. In my own case, I recently replaced the LS3/5a monitors in my study by their most modern descendants, the Harbeth P3ESR. The modern sibling does indeed have more extended bass, and better bass as well (and not just bass - these are truly great speakers), but even so, it is nothing like a true full range speaker. Not in terms of low frequency extension, and not in terms of dynamic potential.
If you want deep bass there are only two possibilities. The first is new full range speakers. The second is subwoofers. As it so happenend I have a B&W PV1d subwoofer in my main system, and one day I decided to experiment and combine it with the little Harbeths. The match was easy to achieve and the sound was spectacularly unreal. You think all that deep bass is coming out of these two litle boxes. The extra power from the sub also gave some more dynamics, even though it still did not quite fill the large main listening room that I was using for the experiment.
So if you are happy with your current mini monitors, I think the subwoofer route is the way to go. If you decide to do this, I have two recommendations, and they both concern room modes. Room modes are the real problem of low frequency reproduction, and they have to be addressed if you want a good integration, and want to avoid boomy and woolly one tone bass. I think you would need to do two things. The first is to use multiple (small) subs - at least two and perhaps more, to smoothen response. See here for an introduction: http://www.acousticfrontiers.com/20101029using-multiple-subwoofers-to-improve-bass-the-welti-devanti...
Have a look at the Audiokinesis Swarm system: http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/
The second would be to add room equalization like the Antimode 8033: http://www.theabsolutesound.com/articles/dspeaker-anti-mode-8033-dsp-subwoofer-equalizer-tas-204/ I have one and I am very pleased.
Combine multiple subs with room eq, and you have the best of what is possible in a domestic context.
However, if you are using mini monitors because your room is very small, forget about all this, and just learn to live with what you have. How large is your room?

Not even one or two really small subs like REL T Zero or the slighter larger SVS SB1000? You can tuck them away in two corners of the room and equalize the boost from the room corner.
For me, the best small high quality speaker with quite decent low frequency extension would be the Harbeth M30.1, but I have obviously not heard all that is on the market. See: http://www.theabsolutesound.com/articles/harbeth-monitor-301-loudspeaker/

I faced similar domestic restrictions and opted for a B&W PV1d to match our minimalist modern interior.
I think the concerns about placement and integration of subwoofers are to be taken seriously, but they can be overcome without too much difficulty. The problem is room modes, the resonances at critical dimensions of the room. With the traditional unequalized single (big) sub, finding the right spot and creating good integration is indeed hard. The solution is simple and twofold: multiple subs (two small ones is usually enough) and room equalization. Two small subs will smoothen the response because the peaks and dips from one sub’s location will not be at the same frequencies as from the other sub’s location. In practical terms, as the DSpeaker Antimode engineer told me, just push two little subs into two adjacent corners of the room, benefit from corner boost to get rid of dips/nulls, and use equalization to reduce the peaks. Using the very affordable DSpeaker Antimode 8033 is dead easy: it is automatic, and takes maybe half an hour, including reading the manual. The result is quite dramatic, changing bass response from woolly and ’slow’ to tight and ’fast’. The Antimode will also equalize the response of just one sub (as in my case) but only for a more restricted listening area. That area gets significantly larger with two. So next on my purchase list is a second PV1d, but that is another story.
I would think that in a medium size room like yours, two small subs in the room’s corners would be visually more attractive than, for example, larger floorstanders (that often also introduce bass response problems). As for SVS, they have a generous return policy, so you are not risking much. Listening to subs and comparing them in a dealer's demo room is next to meaningless, because you are listening to the character of the room rather than the sub.