I don't think an international draft would have that effect. If you look at the domestic draft, bonuses range from ~$8M at pick#1 to ~$1M at pick #60.
I think the international talents who sign in the $300k - $6M range would still sign for the same amounts, roughly. So no change for the vast majority of players.
What you would see is the really elite talents get capped at something like the #1 pick in the domestic draft. So a few of the star prospects that pop up each year, like Moncada, Yasiel Sierra, or Lazarito, wouldn't get any of thee goofy $30M, $16M deals.
It would be weird to see MLB implement a draft where the $$$ was drastically different than the domestic one