Best thing you can do is accurately list all the items you have, with conditions etc. List the country, year and cat numbers if possible.
As a rough guide, your box sets are (in the region of): Gold cabinet £400-500, Complete Works £100-150, Freddie Box £150.
Popsike will give an idea of recent sale prices. You can list here, at the Facebook page Auction This Day, on eBay or Discogs for most things, although there's plenty more.