I want to create a pay pal buy now button that changes the price of my product over time in a preset amount daily. Right now I would have to manual change the price of saved buttons in Paypal.
In the call me crazy department I also would like to be able to link a price (in my case original artwork) of my product to a function that calculates the price of a product (in this case DJIA divided by X times per square foot total size of the painting... but that's just for fun as the fine art market can be very arbitrary in pricing work.
You won't be able to do that with a hosted button unless you're using the Button Manager API. If you're going to use API's, though, I'd recommend going with Express Checkout. You could hook this up to a database or just have your script calculate whatever it needs to dynamically populate the request data including the amount or anything else necessary.