The ingredients:
So you can build a trigger that loads the Google Docs form every 24 hours (for example) and asks you for how much you spent on X. This is automatically timestamped and saved in a spreadsheet by Google Docs, for your charting pleasure.
Here’s the AppleScript required:
tell application "Safari"make new document at end of documents
set URL of document 1 to “link-to-google-form”
end tell