mid-priced transformer for MTH trains ?

Your least expensive option for continual power to the tracks, would be to purchase a new or used MTH 50-1033, DCS "REMOTE" Commander. Your present transformer would supply the power to the Commander base. Then you can use the remote to operate your engines in DCS mode. The engines must be programmed to address number "one", if their address was ever changed by a previous owner, in order to run them with the Remote Commander. Your local hobby shop can do that for you or a friend that has DCS TIU. Remote Commander's sell for around $59.00 on ebay.

I assume you are running Conventional rather than DCS? If so any Lionel or MTH transformer will work fine. I like the MTH Z-1000 because it has a separate 14VAC output for accessories. About $120 new from any of several OGR advertisers (links at the top of the page).

Not sure what you mean by cutting the power completely because that is exactly what any transformer does when you push the direction change button?

Normal to cut power when direction button is pushed

dogdoc posted:

Normal to cut power when direction button is pushed

Highlighting the point that Dogdoc made. Cycling power is how e-units work. You can cycle the throttle on the transformer off and then back on, OR press the direction button. In either case, the ON-OFF-ON of the voltage is what causes the engine to change direction.

I own a MRC Pure Power Dual. The direction button works just like the ones on a MTH Z1000, Z4000, Lionel CW80, ZW-L, et al.

My guess is that your MRC transformer uses chopped sine waves/pulse width modification to control speed, which MTH PS1 and PS2 locos (and perhaps PS3) do not like in conventional mode.  Nothing to do with the direction button in all likelihood.  Best off with either a new MTH transformer or with a reconditioned postwar Lionel transformer from a reputable dealer for conventional mode.  This is what these locos were designed to work with in conventional mode.  Other "solid state" transformers, such as the Lionel RW and MW also gave problematic results with MTH locos in the past.  The use of pulse width modification/chopped sine waves rather than pure voltage change in a sine wave for controlling speed was the culprit, if I recall correctly.

I just picked up a MTH Z-750. Very nice.