I don't know that the gun dealers are loving this. I am sure they would rather make $30 profit on a thousand rifles over the next twenty years than make $90 off of $100 right now with no future ability to sell them.
It is a question of supply and demand. With the scarcity problem particularly acute right now, the market discipline that leads to an efficient allocation of scarce resources drives up the price. That is the way the world works. It is all question of risk and reward. Do you want to avoid the already inflated price on the risk of not being able to buy the rifle at all in the future (or havng to buy pre-ban models after the ban, should it pass, at the even more inflated prices). It is all about risk allocation.
To the Original Question, I would go with the lower, as to my current understanding, for several reasons. One is that you may want a telescoping buttstock, which you could buy with the lower and have that ready in case of a ban, another is that, if the administrative judges decide the same, pre-ban parts will be allowed to be installed after the instating of a ban on pre-ban lowers.
Finally, don't just try to buy the rifle. Fight the ban with all you have got to keep it from happening in the first place.