Hi, I was basing the price range on what dealers online are asking, as well as what ebay prices are commanding. I found a lot more info last night, conclusively connecting this helmet with F/S Charles M. Beattie, who was shot down over Belgium in WWII and made his way back to the UK. Here are documents showing this-
Go here and click "View Digital Copy". I bought the helmet with no history, and carved and written inside is "Beattie C M" and an unknown number above it. While reading through these documents, I discovered that the unknown number is actually Beattie's listed Serial Number. The helmet is not for sale at the moment, but was looking for a value (especially with such an interesting story and the documents to prove it) to put into my collection database.