Hello there!
I've mainly work with google sheets and google apps integration. Nowadays quite a few projects transferring from excel to online sheets.
Usually it is a straight forward process when comes to formulas. However there might be a few questions when it comes to the macros, as those are written in VBA, while google apps script is bassed on JavaScript. Totally different code base, which requires complete rewrite of the code.
More over, there are a few limitations that people sometimes fin puzzling. For instance there are no buttons that you can simply insert into a google sheets. There are ways to design them, but it isn't actually a straight forward process. So normally I would just place any kind of actions related to change of status (button click) into a custom menu at the top if the screen. Concept stays the same but may require a bit getting used to.
Without seeing the actual spreadsheet, it is very difficult to estimate the amount of work. So the price and time maybe be subject of further negotiations.
Let me know if I triggered your interest, and let's talk details.
Cheers,
Denis