Cost are interesting but relative compared to other Tabletop periods. Skirmish is different of course but only if you can keep megalomania at bay and stick to warband sizes
We've been setting up Battlegroup sized units and they roll in at around 470gbp for 2 platoons, HQ, Weapons Sections, MBT platoon, APC Platoon, HQ and support vehicles, so around 80 troops and 12 vehicles. Double that for two sides and I still think 2 platoons is on the top side of what you can deploy and use, a reinforced platoon being about right for a standard table size. Starting up in Napoleonics and getting two sides up at say 8-10 battalions each, 2 cav and artillery would set you back easily the same and probably more but with a much bigger painting problem