What's a good step-up transformer?

The best one I have had is the one built into my Lamm LP2, which gives me 57db of dead-quiet gain and is sufficient to handle a Koetsu Rosewood Platinum Signature, which is pretty low output. In the past I've had both a Koetsu, which is well-regarded but in my case I could not eliminate hum problems and could not use, and the Expressive (Expensive, too!) Technologies, which worked well for me but has its own problems and quirks and is not the best performer in every application--there is a recent thread about that unit here on the A-goN, with varying opinions about it, check it out. My belief is that it takes a lot of work to get the things to work right, there are many underperformers in the area, it does add coloration to the signal path and that in the majority of cases you're better off getting a phono stage with sufficient gain to handle your low-output cartridge rather than using one. Just my $.02.

I've had good results with inexpensive Ortofon, expensive Ortofon, Denon AU320, Fidelity Research, and Cotter. No hum problems with any of them. Their fidelity is relative, but even the cheap Ortofon was more acceptable than some noisy active step-ups. Really isolates the phono stage...

Try a Cotter; many say it is one of the best available. First choice would be a classic Kondo Audio Note tranformer but, as you said, they are not cheap. My recollection is Bryston also sold one that was simply a rebadged Cotter.

Ortofon still makes two transformer models, also (or maybe it is Dynavector). One is reasonably priced and the other is a couple of grand and goes the full silver wire route.

M.A. Cotter is a very good one. Also RWD, and Verion. Jensen are commonly used as built-in to many higher end preamps. Bent Audio sells the Stephens and Billington kits and assembled units. Ortofon, Denon, Shelter, all have outboard units. Lundahl is a common brand of raw transformer for DIY use.

Not "everyone" says that moving coils are necessarily superior. An alternative solution toward the goal of a low moving mass MC cartridge, while combining the benefit of high MM output voltages (no transformer or gainstage required) is the Grado cartridge line. These are hybrids, a variable reluctance design. Very low moving mass + higher output are available in certain Grado models. I favor the woodbody designs, but they also offer some economy models.