Currently MSC is selling the Flexbar magnetic Soft Jaws for vises for $12.99.
You can get less expensive vise jaw liners (such as these from Sears), but the Flexbar soft jaws are a bit more versatile. One jaw has a horizontal vee groove and the other has two vertical and one at 45 degrees for holding all manner of work. They’re made of nylon, which wears well in this application. MSC is difficult to link to for sale pricing so the part# is LR09232208.
Flexbar Magnetic Soft Jaws [mscdirect.com]