For a simple gripper, you can pretty much go to a toy store or a walgreens (or similar pharmacy) and find one.
At the toy store, they are usually sold as "robot arms" or something stupid; basically a stick with a grip and trigger, and on the other end a "claw"; squeeze the trigger, and the claw closes. They are pretty cheap - for instance:http://www.ebay.com/itm/2-ROBOT-PICKUP-CLAW-GRABBER-novelty-hand-toy-reacher-/330560700872
Now - if you go to a walgreens/cvs/pharmacy - you can pick up a medical device that is basically the same as the above toy, but engineered a bit better for use by those to reach top shelves and such - like:http://www.ebay.com/itm/PickIt-Reacher-MEDICAL-BLUE-/110929634306
Words to search ebay with:
"Robot" "Toy" "Grabber" "Reacher" "Medical"
They come in a variety of styles/types. I've even seen them "used" at Goodwill and/or other thrift stores - grandma no longer needs one when she passes away, and so the kids donate it; much cheaper than buying new.
You can use a servo or a strong solenoid (or a gear motor) to actuate it.