Pontos can field some of the heaviest armies in the late game.
try this:
3 classical hoplites
4 medium phalanx
1 elite phalanx
4 syrian/bosphoran archers
1 scythian noble cav(cheaper and stronger than the kappadocians)
2 sarmation noble horse archers (these last two are kinda far)
2 roxolani riders (im using scythian HAs until i reach sarmatia)
1 galatian heavy spearmen
1 elite thracian infantry
1 general

thats pretty expensive, but some units like the classic hoplites and archers are good deals. It hauls a lot of ass

as for cheaper armies, i build entire armies of natives of a specific region. These vary in size but you can easily reduce or increase their numbers if you send them home to rest. for example:
galatian army might have, swordsmen, heavyspearmen, celtic slingers.
thracians might include, light cav and spears, and their elite infantry.
later on you could have a persian army, a greek army, an alexandrian army, and a scythian army. The last of which i find particularly useful, cheap, and quick defence for any part of the empire, a border guard of sorts. You'll have to keep in mind to command the galatians like galatians, persians as persians, etc.