The Morton Portable Glass Shop jig has saved me many dollars cutting stained glass for wetplate. If you aren't going to cut much, just be sure to get a pistol grip type cutter that has an oil reservoir. That will increase your success as well.

A heavy-duty guillotine paper cutter will be OK for metal plates but you might find it worthwhile just to have the vendor cut it for you. I once used a metalworking shear and liked it much better than the paper cutter. The paper cutter has a tendency to bend one corner of each plate. Alas, the $hear co$t$.