I'll agree with Don test before you commit, but we used vacuums on last years robot. They were made from 2.5 gallon shop vacs from Home Depot.
They cost about $25 and we powered them with a FP motor. It was a pretty simple modification. FIRST cut away everything extra except the impeller housing and a little of the flange material for mounting surfaces. The brush mount for the stock ac motor was a perfect fit for the FP motor mount. Then you just needed to turn a shaft on the lathe to mate the FP motor shaft to the vacuum impeller. Here's a picture of the finished modifications. The entire mechanism with hose, mounting hardware, and our final COTS suction cup was under 2 pounds.
I thought this might help if you do want to test vacuum grippers.