Kevin, you're gonna get hosed if you follow the electrician's suggestion. My bet is that the existing range wire - which was just fine a few years ago - has only 3 conductors. That's simply not sufficient to wire a subpanel. Today, the code requires 4-wire to ranges (two hots, neutral, ground). You might have been able to pull that one off IF the wire was sized sufficiently to accommodate the range plus whatever else needs circuits.