If the public DropBox path can be predicted, you can script this using a $file variable to set the path.
If it's not predictable (or may not exist on some client machines), you will need to let the users find their own Save To location with the dialog.
You could also use ErrorCapture when saving to the predicted path, and, if there is an error, provide a save option with the dialog enabled so they can pick their own location only if the default path failed.
Can the path be a link to a web site? (not to a folder on hard drive?)
No idea -- never tried such a thing
Is the target path predictable using an IP address?
Are there going to be any permissions issues reaching the site's folder?
Would love to hear what you find out when trying this.
This may help you:
1) I use the function Get(DocumentsPath) followed by some text function calculations to parse/paste the path to a specific named folder on my desktop. Store the path as a variable and use it for the "Output File Path" on the SPECIFY OUTPUT FILE setting of the "Save Records as PDF" script step.
2) I save FM-generated PDF files to my desktop and then run an automator (Mac) script to load a dropbox folder. This can also be done manually or with some other app.
The step above (using FM to create the PDFs) works regardless of the computer used (PC or Mac) since I use the Get(DocumentsPath) to create the "Output File Path". Any computer-specify quirks in the path can be removed with the text calculations.