Hi Andreas,
For RW you will need additional ERP system + license for ILM.
You may migrate this ERP system to new low end server. Keep this database read only
Many customers go with this approach. This will save some cost on high end server while you still have old data maintained with you.
You may keep this DB and application down to save on power and resource requirements, Make it up only when required.
Hope this helps.
Regards,
Deepak Kori