How can I create a photo collage without it breaking me?

Even by hand, this is a pretty quick & easy job. Set up your main document blank (300 dpi ought to be fine), use snap to grid, import each photo to a separate layer, resize each to the correct size & drag into position on the grid, apply a drop shadow style to one layer, tweak it until you're happy, copy the style to the other layers and you're done. Export to PDF for a file that can go to the print shop. Maybe an hour or two total.

(ps Although the contact sheet builder is cool, if you are a perfectionist you will spend way more time tweaking its parameters and rebuilding the composite over and over again than if you just do it by hand.)

Use the actions pallet. It allows you to record any series of actions and play it back. Basically you make a new action, hit record then do your stuff, then hit stop when done. So in your case I would do something like, resize the source image, select all, copy, switch to the composite image, paste. Repeat for all 12. Then I would have an action for move one spot over. So record an edit transform move. Bind it to a short cut key and repeat for each image. You can also select multiple layers apply it to the group, then just unselect one layer at a time and continue moving it over. Last I would apply the layer effects you need, then just copy layer style and paste it to each layer.

Download a trial of InDesign instead, mathematically figure out how big you want each portrait to be inside the picture, make a bounding box of exactly that size, step and repeat it for 11 copies in a grid exactly where you need, place each sequential picture in a bounding box, apply drop shadow and save it as an object style and then use that drop shadow object style on all of the bounding boxes to be perfectly identical. You can also use the Align palette to distribute all of the images evenly on the page, or put a specific amount of space between them, or group them all and center them, etc. Plus it exports PDFs that are a fraction of the size of Photoshop's. Photoshop's great at manipulating photos, but it's not the best tool for layout. If you must use Photoshop, you can make each picture the exact same size with the Transform tool, align to a grid as was suggested above, and then the CS6 trial should have the ability to align exactly with the move tool (just have everything on a separate layer and then select the layers you want to align). You can then copy and paste layer styles once you get a drop shadow you're happy with.

Late to the party, but in case anyone is following this thread and wants to do this type of photo collage quickly and easily without using Photoshop, you might like http://zykloid.com/posterino (Mac only). It often goes on sale as part of various bundles right before the holidays, so keep an eye open on places like https://www.mupromo.com/.