I like where this is going, but lets keep a few things in mind.
You are adding units to the board, that are “worth a hit”, for $1.
For Example, I am russia, I buy 37 entrenchments first turn. Turn 2 I do the same.
OR, if I am SBR’d to death, and my capital is at risk, I spend whatever I’ve got on entrenching my infantry, DOUBLING the amount of units that can be hit.
You are now fighting units that can produce anywhere, at $1, in a game that already favours the defense. (It’s why infantry defend at 2) This has nothing but room for exploitation, even sealion, or the capture of Egypt, are totally off of the table.
Why not sell $4 infantry that are worth two hits? I’ll tell you why, because it’s a bad idea.
You also must note, that the purpose of tanks, and artillery, were to BREAK entrenchment. That needs to be encompassed or included in this rule, perhaps each tank, or artillery, freely negates an entrenchment?
It would be much better to see a new piece, called a land fortification, or trench system, that you could “fill up” after building, much like a transport, that either offered your units extra protection, at atleast a $2 a hit price, or retained other abilities, like preventing 2 enemy tanks from rolling each turn or something (Idk).
you could then spend $6 on a place like egypt say, and have a trench system, that you can load 3 infantry into. That protects them from hits by infantry, or takes an extra hit for them, or reduces attacking artillery to 1, or something.