
Amazingly, Photoshop/Imageready don't have a readily apparent way to set up a batch action that says, "Take all the files in this folder and optimize them to 70K".
I was lucky enough to find a Solution via Google Groups, but since I haven't really seen this mentioned anywhere else it bears repeating.
In ImageReady, open an image and create a new action called, say, "Optimize to 70K". The action will start recording immediately. Click the "optimize" tab in the image window, and then in the Optimize palette menu choose "Optimize to File Size", and enter 70K as the desired file size. Click "OK", and stop recording the action. With your new action selected, choose "Create Droplet" from the actions menu.
To trick ImageReady into letting you use the "Optimize to File Size" step in a droplet, leave ImageReady running with an image file open... otherwise you will receive only "Optimize to File Size not available" errors.