Check out the Paradigm Studio 40's.
The GMA Callistos have better bass than the Europas (lower and more detailed) -- I have them in small room (12.5x15) with no sub and bass is engaging and appropriate. They're at the upper end of your price range, but there's a pair used for sale here and maybe you could get close. I haven't heard the others you mention, but I have heard the Paradigms and the Callistos are just more musical and compelling. Good luck!
Lucifer here. I get excellent bass response [~40 Hz] with my SEAS Cygnets from Madisound. The ancillaries are a little over the top [P300/Delta/SF/Muse/Thule/Bel Canto] for a budget speaker, but they bring out the best in this modest but well-evolved design [cool phase plug, inverted drivers, LEAP xover, and a highly "listenable tweeter"]. Cheap and cheerful as they say in the UK, but the sonics are full and rich, musical and satisfying. If you put music before dollars, the results are sometimes better than would be otherwise. Danes don't lie, and neither do Norwegians.
Just remembered these http://www.morelusa.com/home/mlp-403-5.htm
Any outfit making their own drivers has got a leg up on most other speaker makers. Sealed box equals good bass definition, if not 20 Hz at 110 dB. I like the big dome midrange and the 3" voice coil on the woofer, you might too, at $600 shipped. Best of luck and enjoy the ride.
I am a monitor freak. I have had many including,
Joseph Audio RM 7si
Totem Dreamcatchers and Mites
Von Schweikert VR1
Tyler Acoustics Taylo Ref Monitors
AVI Neutron III
Aerial Acoustics Model 5
etc, you get the picture.
I finally found some that I may keep forever. You should check them out: North Acoustics Spirits. They do everything right, probably the best I ever heard.
Check Northacoustics.com you will see a picture of my actual speakers, made for me upon order. George Short (owner) is a great guy and a knowledgeable speaker builder.
I love my Reference 3A MM DeCapos. I stole them here on AudiogoN for $1000 for a perfect pair. I couldn't be happier. They replaced a more expensive speaker (from Muzikat's list!) and are better in every respect.
Plus, the DeCapos have one huge advantage over most other monitors. They are very easy to drive and can easily be powered by almost any amp. I've used them with as little as 1.5 watt/channel 45 tube amp and regularly drive them with my 3.5 watt/ch. BottleHead Paramour 2A3 tube amps. Currently I'm using 40 watt Channel Islands VMB-1 mono-blocks.
Bass is excellent for monitors. Great bass definition and extension. I love 'em!!
you might take a good look at monitor audio gr-10. i currently have a pair of paradigm studio 40 v.3's. they are fine sounding speakers but lack a bit on the low end. they could use a sub, which i hope to acquire in the spring. i have a pair of monitor audio bronze b-2's for my second system in the basement. they have a very good low end. the gold series gr-10 should be worth checking out. they list for $1,500. i noticed there are a pair on audiogon classifieds for $750. no, i don't know the person selling them; nothing in it for me.