The cost isn't based on stats; both cost and stats are derived from size, status, equipment and so on. I've posted the formula before, there's nothing mysterious about it:
Code:
A: values 1 through 4
- 1 = levy
- 2 = regular infantryman and light cavalry
- 3 = elite infantryman and regular cavalry
- 4 = elite cavalry
B:Addition of armor values depending on unit
- helmet +1
- 1 greave +0.5
- 2 greaves +1
- soft armour +0.5
- scale shirt, and linothorax +1
- mail +1.5
- breatplate +2
- cheires + 1
- small shield +0.5
- large shield +1.0
C: weapons
- sword +1
- spear +1 (including kontos, sarissa, xyston)
- dagger +0.25
- longsword, kopis +1.5
- rhomphaia +2
- sling +0.1
- simple bow +0.25
- recurve bow +0.5
- javelins +0.5
- longchai +1.0
- pila/soliferra +1.5
- axe +0.75
- club +0.5
D: 2 through 3 based on green through elite
2 = levy/green and skirmishers
2.25 = militia-type units, drafted regionals, or semi-professionals
2.5 = regular
2.75 = veteran
3 = elite
F: Number of men in unit on normal setting
H: horse type
Camel = 5.5
Pony = 6
Horse = 7
Nisaean = 8
1/2 barding = +2
3/4 barding = +3
full barding = +4
Equation:
cost = F[D(A+B+C+H)]
Upkeep is 3/16ths of recruitment cost.