Hi. I've been given a very complex Excel workbook that contains a dozen worksheets and hundreds of calculations. I need to create a web interface where users can answer a bunch of questions, in effect filling in selected cells in the spreadsheets and getting a summary based on all of the calculations.

It will likely depend on some specifics that I don't yet have, but in general... is this type of thing best left to some sort of online spreadsheet program? Is it crazy to do this in PHP/MySQL? If a spreadsheet program is best, what, in your experience, is the best one? Preferably free. :-) I assume there's a way for users to save their data and be able to access it later.

Thanks in advance for any thoughts.