I think I just replied to you in another thread, so sorry if this is a duplicate.
If you go to http://flyboynaturals.com/suqu.html there's a pic that shows the amount of petals per square foot for various levels of coverage (from scattering to carpet ). They also sell them, so you can get an idea of what they cost - I'd look in the "Brides on a Budget" section....
Disney doesn't allow outside florists at outdoor venues, so you'd have to bring your own if you don't pay Disney. I'm notoriously cheap, but even I paid Disney just so I wouldn't have to ask my guests to scatter the petals. But it seems like this would be easier for guests to do at a location that isn't in the parks like ours was...
I told the Disney florist the amount I wanted to pay, and she decided how many petals that was.
Here's what $50 worth of petals looks like in the Morocco Pavilion's aisle. Your results may vary....