Good night,
I am not familiar with Google sheets, but if you want real time price data and you have the last version of excel, you can obtain the same data, and the organization of the data would be much better.
Regarding the pop-up window, I have an idea of how it could be done in excel with a VBA code. If you want to assign me the project, happy to do try help you tomorrow morning. Let me know if you are interested.
To see what i mean, I have created this little sample, in which you can for example add the amount from the bottom that you required for the cell to highlight):
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It is an excel file.
Happy to talk to you, kindest regards.