4Mbit (512k x 8) is the largest they offer with SPI.
The larger ones are parallel with a larger form factor.
$17 to $27 Digi-Key depending on speed and temperature rating.
It appears that there are 8Megabyte MRAM chips available at Digikey at about $50. Everspin is the brand we have been using. I think they invented the technology.
Burns Fisher, WB1FJ
AMSAT(R) Engineering -- Flight Software