See also Five-Score Monthly.
Arriving at values for this title in the UK and the US is tricky as sales are few and far between and the collecting market I suspect is small outside Australia.
I have collected a few copies of this title over the years, mostly fairly early ones in the number range from about #15 to #54, mainly for the Late Golden and Silver Age DC reprints of Superman, Batman and Superboy in black and white and great 'World's Finest' Superman/Batman/Robin covers. In the later 1960s the covers became more Detective and Action Comics reproductions. For mid grade Fines and Fine Pluses I was paying £30 or so in the 1990s. I had a few higher grade copies and paid £40 even £50 for them. If I sold them now, I would expect to at least get twice that back. What would a #6 (#1) issue fetch? £150/$200 in VG at least as it is so scarce.
The very early issues of Colossal Comic are pretty tough to find and very rarely come up for sale. The few collectors that want them I am sure would pay well for them, in the hundred/hundreds of pounds/dollars to get them. A look through Australian eBay would probably shed light on current values.
Note past eBay UK sales: #31 sold in VG on eBay UK in Jan 2008 for £22. A #30 in VG sold for £27.78.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.