The last 4 are the hardest to lay hands on and it's difficult to say which one is the rarest of them all or even how they "rank". I'll give you my own experience with this, but I'm emphasizing that's just one opinion. I'm sure other people may have had different experiences ...
In my experience they should be put in the next order of "rarity": Scooter
, Sweetums, the Swedish Chef
and finally Sam the Eagle
The rarity may have an effect on the price again, but that's not necessarily always the case: I paid my Scooter just 5 EUR even he's tough to find, Sweetums 7 EUR, Chef 10 EUR and Sam a whopping 12 EUR.
I guess then that a full set should top up the price a bit more still, because ... well, hey ... it's a full set so you don't have to go and chase down individual figurines anymore and that's always worth something too.
I'd say that a full set would be fairly priced 80 EUR if all of the figures are mint, near-mint.
Well, lenghty answer ... I hope it helps.
I'd love to hear reactions to my "price guide" here.
And oh ... sorry, but I just had to use EUR everywhere because that's what I'm used to. You can easily google the current exchange rate to translate that to dollars, aye?