The Gunsmith I associate with has used these from Brownells day in and day out for decades:
http://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/vises-accessories/vise-jaws/elastomer-pad-for-multi-vise--prod22186.aspx
They're a little on the expensive side, but they do work very well.
On the cheap, you could buy a Truck Mud Flap from any place that sells Commercial Truck parts for as little as $9.00 cut a couple sections, then glue them to a piece of angle Iron.
On a tangent: Buy a good vise, and I mean a really good American made vise that will serve you well the rest of your life. Secondly when you do, find a Shop that supplies Metal and buy at lease a 1/2" plate, preferable 5/8" or even 3/4" then drill the plate for the vise and bench bolts, additionally for a good many benches it's best that you match the plate holes to bolt through the bench, sandwiching the bench top.
On another tangent while you're buying plates, have one cut approximately 8"x10" then drill & tap holes to mount your reloading press; I have one with multiple holes and sizes to accept everything from a Pro-1000 to the .50BMG set up (the .50 puts a LOT of torque on the bench top and bolts)
A chunk of 5/8" mild steel plate isn't all that expensive, neither are a couple of drill bits, and taps, however a Drill press IS a must!