Best Cheap Amps for Magneplanar Speakers

Look to Wyred integrated amps. Match well with my .7's. I've owned several pairs of Maggies over the years. I will tell you this, the more quality "power" the better the sound. This may be true with other speakers but never as much as Magnepans...

If you are truly looking for a cheap amp....
$400,  I like the Old Sumo Andromeda II or III...(III might be $500)
$900,  I like the Muse Model One Hundred Sixty
These will both make maggies sing

I don't know what you call cheap, but I have had $300 qsc 1450 behind mmgs, and it put out clean, undistorted sound at concert level.  The lights in the house were dimming with pounding bass drums. I had an adcom preamp between source and qsc.  Mmgs were without fuse and sounding good, and the qsc was not even at 1/2 full volume.
It's cheap, something to try.

Class D SDS 470c can find them used for around $400.

Magnepan like many less efficient speaker makers do not emphasize the benefits of more power with their products probably to not limit market or discourage customers.   Less watts will work but you will run out of juice if the volume needs to go up.    Current probably does not hurt but I did find Maggies not as needy there as with many less efficient dynamic designs.  Tube amps even work well if powerful enough to get the volume you want.

My local dealer has sold Maggies for years and recommends Class D amps by Rogue for use with Maggies though they sell tube amps also.