Unit pricing is a bit of an art, there’s not really a universal formula for how many PU each stat or ability is worth. Generally it’s a good idea to start with your cheapest general purpose combat unit which players will be purchasing in the largest numbers (in A&A, the Infantry) and use it as an anchor to balance the rest of your roster against. Because for every more expensive type of unit, the question players will ask themselves is “why should I buy this instead of an equivalently priced stack of infantry?”
Fighting effectiveness is something that can be calculated. If you tell an AI that you need to calculate how often 6 Infantry beat 3 Tanks in battle on offense and defense, it can give you the exact probabilities once you’ve provided all the unit parameters. Whichever unit wins more often for the same IPC investment is the more efficient in combat.
I could go through a long list of examples to prove it, but I’ll just summarize and say that of the four basic combat stats (HP, attack, defense, movement), HP is king when it comes to combat efficiency, specifically HP per IPC. And when all the land units have 1 HP, a stack of cheap units is almost always favored to win against higher priced ones with more attack/defense. The only things that can really shift the balance in favor of the elite units over the swarm is if they have multiple attack rolls, multiple HP, or special abilities that disable or debuff some of the enemy units - which none of the land units in A&A have.
But combat efficiency isn’t the only thing you’re paying for. Movement is obviously another. Fast units should not be as cost efficient as slow units (otherwise no one would buy slow units) - you pay a premium for the greater responsiveness you get for extra movement points.
How much that extra movement is worth depends heavily on both the map size and the overall unit density. Extra movement becomes more valuable on larger maps, and blitzing capability is most useful on maps with lower unit density (leaner starting forces and relatively lower incomes).
Then you have all the other abilities like support, AA, etc. these are valuable for creating different role archetypes - jobs one unit can do better than any other unit. In A&A, Infantry’s role is to be the basic line holding and HP filler unit. It is the most efficient unit to buy for defense and to sacrifice as a casualty. Artillery’s role is an enabling one that turns the Infantry into an efficient attacking unit as well. The AA Gun is crap for most purposes but the only unit that has a chance to bypass screening and snipe powerful air units before they can fight.
The Tank delivers poor combat value for its price in A&A, but still has a role it can fill because it is fast, capable of blitzing, and individually superior to a lone Artillery or Infantry - exploitation. The Tank is good for seizing poorly defended territories. It’s bad for fighting in large scale battles on its own, but it can be used to tip the balance between two fairly evenly matched stacks of infantry. In wide fronts like Russia, tanks have multiple avenues they can attack from, which forces an opponent to spread their defenses or leave some areas uncovered. One Tank costs the same as two Infantry, and usually loses if it attacks them, but if your opponent has to put them in two different places to cover the Tank’s possible attack avenues, then the Tank has favorable odds to beat either of them on their own. So in the right environment (areas with a lot of provinces), the Tank makes up for its inefficiency in combat by threatening many areas at once.
The land and naval combat systems are self contained and relatively easier to balance. Air units are the hardest ones to get right because they interact with both systems - you might fine tune it to be in great balance with the land units but then find it plays horribly with ships, or vice versa.
And the base game does far from a perfect job at balancing unit capabilities against prices. I could go on a really long tangent about all the things it did poorly. So use basic A&A as a benchmark you don’t want to do worse than, but not as a shining example of balance done right.
Basically, at the end of the day, you want to look through each unit on your roster and ask if there’s a good reason players would pay the price you’ve set for it instead of buying something else. Does every unit have some niche it can perform better or more efficiently than all the others? If any of the units have overlapping roles, what traits set them apart - do they both have at least one distinct strength over the other, or interaction bonus with different unit types?
