Congratulations !
I assume it's an Emax, not an Emax-II ?
If it is a true Emax PLUS SE, then 40 EUR is really a bargain, because that PLUS model is very very rare.
Do you have a PC with an internal floppy drive ?
In that case, you can simply download the Emax Plus OS from the Yahoo Emax Group or from
http://www.emxp.net/Additional_downloads.htm.
Format the DD floppy disk with EMXP (
http://www.emxp.net) and copy the downloaded OS to that floppy disk, again with EMXP.
For formatting and writing Emax floppy disks on a PC with EMXP, you will have to install the OmniFlop driver first.
It's all explained in the EMXP manual.
You can also order an OS floppy disk on some websites (like
www.route66studios.com), but I have no idea about their quality of service and speed of shipping.