The GM would be rolling the same dye as the player, however as you've pointed out
smaller ranges make targets harder to hit. So I could keep the contested rolls but flip the
dice ranges (ie d12 for easy, d4 for impossible).
But a cleaner mechanic is what you suggested. Using points to increase dice size gives the player
better chances. Might work it so bids increase dice, but skills just add to your roll.
Still thinking/tweaking so as I figure it out I'll post the revised mechanic