New Phono Pre-Amp

A Black Cube, Musical Surroundings Phenomena, or Trichord Dino, would be candidates in that price range.

If you decide to audition or buy the Black Cube, I strongly recommend you get the Black Cube SE with the new, larger power supply. I have owned both, and the "SE" version is a significant improvement over the original model.

I spent only slightly more than that on my used Camelot Technology Lancelot, which Fremer rated above the others mentioned FWIW (it sells for about $900-$1K new). It's battery-powered BTW, something which I suspect is a very canny design choice for a phonostage, and permits relatively easy loading- and gain-resistor swaps. It also sounds great, to me. Somewhat unwieldy physically however (2-chassis, though not too large), and it ain't exactly beautiful to behold. Excellent supportive company to deal with concerning any eventualities, and made in USA.

If you look long and hard enough, you might find the EAR 834P at that price...it's a cut above the units mentioned thus far, and has that "tube magic".

I bought a Monolithic PS1 with power supply and it has been wonderful with my MMF-7. I wanted to keep the price in perspective and it is a good place to start. Happy listening :-)

Another option is the Monolithic PS-1 w/ the outboard power supply, the HC-1. I've seen this combo for sale here on Audiogon for 400$. Hard to beat at this price point. While I haven't personally compared this combo with the Black Cube, a number of reviewers claim the Monolithic combo is superior.

if you try hard enough you might catch some ear834p used that is superior to phonomena or black cube.

I'm going to second the recommendation for an EAR 834P. If you can afford to stretch your budget to around $600-650 you will be stepping into another league. I've been using one of these for some time now and you cannot beat it for for anywhere near its price. A high-end product that is suitable for very high resolution systems. You have to step up to something like an Audio Research PH3 in beat it. By the way, it is rare, but I've seen these on Audiogon for around $500-550. They go fast at that price though. Good luck and take your time.

I have an MMF-7 turntable and am using an EAR 834P. It sounds terrific; far better than when I was using the Musical Fidelity X-LPS phono stage. If you can stretch your budget $100 or so, then hold out for a used EAR 834P. You'll be glad that you did!