Tracy,
This is a common question asked here on VAF. If you keyword 'hourly or project' and 'what to charge' in the search area you will find prior threads to review in the category in which you posted
Rates and Billing.
I always say that if you don't know if the project is 'cut and dry' then you will need to run a test and see how long it takes you to do a few within say, 10 or 15 minutes and then determine what you want to make Xs the time it took you to perform the work. This would be your project fee.
Clients see value in flat-fee projects so if you can quote a project rate, then I suggest you do so.
If you feel that the project is not 'cut and dry' as you say and will require phone calls, then you can charge hourly for the extra items in addition to the project fee.
So my best answer is to quote the project for the spreadsheet work and then quote hourly for the extra work such as phone calls and research.
The important thing is to be clear about what you will do for the flat fee work and to list what the hourly work will be as well.
You don't want to present a time sheet or a synopsis of the work if there are surprise tasks you had to perform that the client didn't know about in advance.
Janine