River Song Gun

http://hordriss.deviantart.com/art/River-Song-gun-Dr-Who-Prop-256523252

I think Lauren would like this. Two lasers, one low power for targeting, the other 1W IR. You could pop balloons with it. The other option (or in addition) add a small combustible source and a weight and you could simulate muzzle flash and kick back.

For the body follow this. Get the base shape in Blender, convert it to a paper model and glue onto poster board. Construct the model and coat with Bondo. It should disassemble into a few parts so I can access the electronics and change batteries. After the base is roughed in, use additional Bondo to model the details by hand.