Question about non-cash donations

[Cyryl]

I recently looked through a small box of donations left to our parish and found several old British Sovereigns and some silver Crowns. I expected these to be simple to log as standard currency but the face value is obviously nothing compared to their actual weight in gold or silver. Our vault has been humid lately so I noticed some spots starting to form on the Victorian-era pieces which is worrying for their preservation. I tried looking up some values online but honestly I'm a bit lost with the different mint marks and conditions. I want to make sure I record the correct "fair market value" in PowerChurch for the donor's receipt without making a huge mistake. Has anyone here dealt with valuing a numismatic collection like this for church records? I'd appreciate seeing how you handled the appraisal part.