Using iCloud with iPhoto without upgrading to iPhoto 9
As outlined in this question, a workaround does exist, but it's ugly.

You'd need to run a virtual machine running Windows (I'm not sure if you could do it with Wine, or if you'd need an actual copy of MS Windows (which is much more expensive than $16). You then download iCloud Control Panel from Apple and install it on your virtual machine. Then, you can use it to send photos to iCloud.

So yes, it can be done. But you're likely better off spending the $16.