I can't believe what guys are asking for these Donald Ducks. $40-$50. I'm not sure they're selling many for that. Kids definitely like them. I don't believe the pink hue adds any value. A couple of full ones like your recently sold for 35 plus shipping. I don't know...
I'm surprised they aren't worth more, I would have thought the cross-over appeal would drive it up. We've got Felix the Cat bottles up here that go for ridiculous prices, like several hundred dollars for the paper label ones despite not being particularly rare. I guess the Donald Duck bottles must be a lot more common, or Felix has more of a devoted collector base.
As for price guides, there are a lot of price guides out there but I've never seen one that was close to being correct. The good bottle guides are often decades old and when I had a modern Kovel's book several years back the prices tended to be completely fabricated, with common bottles listed as being worth $300 or so. For pricing the best resource is Ebay's "sold for" feature but otherwise it's more something you get a feel for over the years. Prices can fluctuate a lot, so it's always a rough guess what something will sell for anyway.