https://www.rme-shop.com/acatalog/RME-S … parts.html
The cost for a PSU for a 19" unit around €100.
Then the typical cost for a technician, around €80/h.
Turning on/off creates most stress for units. Leave space between devices to enable for a little air flow so that heat doesn't pile up between devices, as you mentioned already.
Start with a repair budget of €100-200. Pay €5 or 10 monthly by standing order, then if you're lucky, you'll also get some interest, and after the first replacement, you'll already have a reserve for repairing the next device. When does something break anyway? And if it does, it's usually just one device.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14