Go to Sears, Tractor Supply or Northern Tool and get a Heavy Duty 4" Vise for around $45.00
Then get a thick nylon cutting board and make you some Protective Vise Jaws using the screws in the vise to attach them. Just countersink the holes a little. You can mount it on a board using carriage bolts from the bottom up and washers wing nuts to tighten the vise on the board. Followed by, get you two 4" clamps and you can clamp the Vise and Board to a table or work bench and it is totally portable. It is heavy enough to even barrel rifles.