Need advise regarding small bookshelf monitor

Pricing -- in the $3-500 range. Keep the recommendations coming as I'm not familiar with bookshelf speakers as have never peaked my interest -- these would be for my sisters' system & I don't have a clue as to what amp they are using -- probably along the big box store line; i.e., Yamaha, Pioneer, Sansui, etc.

$300 will get you a new pair of Epos ELS 3s. I actually have a pair at my office in a bookcase, they work quite well there. NAD receiver is the power.

Energy Loudspeakers manufactures some good bookshelf monitors at reasonable prices. I had a pair of the Take 5's for a while. No bass but good for a 2nd pair in a small office or for surrounds. They have a C-100, C-50, and RC-Mini that will fit your space requirements. I was going to suggest the Proac Tablette 8 Ref speakers which will fit in your space but they are a very high priced speaker line out of the UK. Even their small units are way up there. B&W produces some mini-monitors such as the LM-1 and M-1. I have 3 of the M-1's as my surrounds and center channel. Super sound but again, no bass. The M-1's I believe sell for $200.00/each.

I bought a pair of Usher S-520's for a system for my daughter and have been very impressed with them. They're small enough for the entertainment center, are front ported and cost $400 new. Here's a Stereophile review.

Fantastic Amphion Helium 2. There are some on agon for ca. 600$. Won't be disapointed.
Check Stereophile review, is ok, I know these speakers.