I have the same problem
1) format, as learn on my own, like just 1 will lead to prices 0.01, the right format is "1 . (point) 00" - And I think it would be better to specify it on Pricing and Options section.
2) the size of my port (about 3000 and it will be more) - script can on my side process only 600-700 images at once and then broken, I can't choose which ones images to process so I have filling that it goes round. Ok this is a problem of server, but we need to solwe it. For example the script can update pics consequently or using filter.
OR alternatively you can add setting price to bulk edit pictures operations, where we can select pics which are affected by it. Any way - to select pics for different pricing is a good for marketing purposes also.
As for now it is absolutely impossible to change prices on my port - I've tried it over and over two whole days already with few results.
UPD
OR the third way - just add setting new prices (which are defined by author in author options) to bulk reprocessing images action in RF images - All images view.