Here’s a good thread on bidding
Basically it boils down to how many units & IPC does it take to balance the game out.
Against a great player, you might need more…
I take it as I’m willing to play Axis for X IPC.
Also with heavy bombers, others use LHTR (Larry Harris Tournament Rules) where the most damage bmbs can do is limited to the total IPC value of the territory, some use 2X. Yes, heavy bombers using OOB (Out of the Box) rules seem unfair but it’s still possible to win if you can go after the bmbs. Deny the bmbs places to land, if all US/UK are buying bmbs than there is less ground troops, etc, etc. Finding the right balance, but even than I would suggest going with the bid, and a few minor changes. Take a look above LHTR is stickied.
Good luck and Good gaming!