I've done some research and written a paper on the subject. PM me and I'll send it along. We have had some semi-serious testing of phono stages here:
http://www.audiokarma.org/forums/showthread.php?t=522082&page=15 starting at Post 213. You may want to read through the whole thing, but it gets better organized after Post 213 ...
The bang for the buck comes in flavors. For those with fixed arms who do not swap cartridges, the choices are a bit wider. For those with swap-able headshells who do cartridge swapping, the options need to include more loading selections.
The baseline seems to to be the ART DJ Pre. It has been used with a SUT and Moving Coils (MC) up to the $500~$1K range. And a slew of Moving Magnets (MM) up to the $700 range. It's not perfect, but works well for some. Sort of equal to the ART, but different are the TCC 750/760 models.
In terms of SQ improvements, the next tier up is the Ray Samual's Nighthawk, Project SE, Cambridge Audio 640 (with mods), the DIY's mentioned and the Rod Elliot ESP P06/05.
Then we seem to jump up to the Phonomena. From there the sky is the limit and so is the budget. A modd'd Jolida JD9, an Opera Conscience, a Budgie and like, turn in stunning results but take some time to get right (mods or tube rolling). These are well above your budget, but there are sonic benefits that I have heard. I now have a Phonomena because I have heard it for myself, and I own and have used a fair bit of the list I have mentioned so far.
My used record collection and my TT's & cartridge library all seem to have plateaued at the Phonomena level. Others have gone well past me
