I'm not going to comment on prices, but just letting you know this...

+ Sunstorm is the only Rainmaker officially done in the G1 mould (and was reissued)
+ Acid Storm, Sunstorm, Bit Stream and Hotlink are the only Rainmakers to have been officially made in the Classics mould.
+ There's no such thing as Smallest Transformers Rainmakers. If you see any, they're fake.
+ Only Sunstorm and Acid Storm have been/will be released as Masterpieces.

Be aware that there are fake Rainmakers floating around, so I just wanted to give you this information to let you know which ones are legit. Best of luck.