Make vice jaws, though for a quick/dirty solution, you can use your set of hole saws to make the right diameter in a couple pieces of 2x4 or 4x4 wood clamped together, that don't need rigidly mounted to the vice, just to sit between the jaws and work piece.
Do you even need a power tool? How much are we talking about, enough that sandpaper by hand won't work? I mean if it's going to be repeated in the future, then do make some vice jaws.
What is the budget for the bench grinder? You're not really going to bog it down with a wire wheel on tubing, little pressure needed for paint and epoxy removal. Something 8" with 1/2HP in a major brand new, or used, depends on your patience. It's hard to get "too much" grinder so I would be forward thinking about other long term uses.