It depends what style of flash application you are trying to build.
Is the website to be arty "nonsense" or is it to be of actual use?
If it's to be a fully functional website you may want to consider using Flex instead. Flex is basically flash; the Flex compiler will produce a flash file for you. http://www.adobe.com/products/flex/
I think there are various Flex development programs out there which are probably free. Adobe have a paid for version called Flash Builder (http://www.adobe.com/products/flashbuilder/). You can use the trial version for 60 days. I'm sure you're clever enough to figure out how to get a licence.