I got tired of doing the math over and over again in my head so I did the simple math for how much you save using each enlist. Helpful for deck-building and opening strategy.

[I know this is simple math, but sometimes taking a step back and seeing things this way helps]

35g Savings
Enlist Infantry Unit
Enlist AA
Enlist Artillery
Enlist Light Tank
Enlist Recon

40g Savings
Enlist Two Infantry
Enlist Heavy Tank
Enlist Fighter
Enlist Heli
Enlist Infantry and Recon

45g Savings
Enlist 2 Recons
Enlist Recon and Artillery

50g Savings
Enlist Two AA
Enlist Two Artillery
Enlist Two Light Tanks
Enlist Heavy and Light Tank

55g Savings
Enlist Heli and AA

60g Savings
Enlist Fighter and Heli

65g Savings
Enlist Two Heavy Tanks
Enlist Two Fighters
Enlist Two Helis

80g Savings
Enlist Four Infantry

150g Savings
Enlist Seven Infantry

do people actually follow these? i usually just use whatever i can afford

Well in constructed if you know you want an Infantry, a Recon, and a Artillery and you have room for one enlist, this list helps you choose to take the Enlist Recon and Artillery for 45g savings over the Enlist Infantry and Recon which only saves 40g. Not a huge deal in the big picture but still worth the consideration.

This is obviously less useful in sealed where you have to work with what you get.

Edit: Also you can see top constructed players employing this information. For a while last month Witcher was using a deck http://www.battledexgame.com/game.php?game_id=23657 that had 2 Enlist Two Light Tanks and 1 Enlist Two AA, all of which save 50g each. Economics do make a difference.