When I did mione, this is what I found to be the best "cheap" alternative:

Shell 3353 is 236.12 certified. I bought a case at $9.26/qt. The container doesn't have any "generic" ATF statements. It specifically states: Meets MB 236.12 spec for use in MB 7-speed transmissions. Also for use in older 5-speed auto trans. Backwards-compatible with 236.10 fluid.

It appears this is the OEM fluid just not in MB packaging.