I was able to get my hands on a *HP ProLiant ML350p G8 Server from a corporate environment. The company it belonged to went out of business and the proprietor gave it to me. As I already own a home server and this machine would be overkill for my need anyway I would like to resell it. Which price should I ask for?
Stuff like this can be hard to value - it's worth what someone will pay for it. Are you able to check its serial number on the HP website to see its date of manufacture and if there is any remaining warranty on it? There probably isn't but worth checking as it can add value.
Have a look on eBay for any similar servers with dual socket Sandybridge motherboards and also HP Z820 workstations which are not too dissimilar.
As @BGL said, it's only worth what people will pay for it. Which for people on the second drive hand market is usually too high a price. People who want the new equipment will buy new because of the support. Whilst those looking for something cheap... Well this sort of thing maybe a tad expensive. One thing I will say is the tape drive is worth a fair old pop by itself.