I don't know if it will fit or work, but most folks upgrading to an electric fan setup (either upgrading an existing electric fan or a standard mechanical fan) opt for the 94-99 Mustang fans, Ford Taurus fans, or Lincoln MKVIII fans. These eletric fans push out some really decent CFM's and are easy enough to install. You would need to modify or make your own type of hardware or hangers to get the fan installed, but for the most part it's pretty simple. These are also big enough to fit onto many BMW applications.
Like I said, i don't know if that is helpful to you or not - but most of the above mentioned fans can be found in many junk yards and the going prices on them are anywhere from $40-$75... which beats spending $150+ for an aftermarket eletric fan.
Also, with regards to the original electric M42 fan, I thought that just the motors can be bought separately? Did you try searching for just the motor? You might even want to ask around for those parting out cars for a used motor assembly, even that would be cheaper than buying a new unit.