Playing my first game with Romans v phalanx on Friday, so looking forward to seeing how it works (or doesn't) myself.
Jeff Jonas wrote an interesting article on the interaction of maniples v phalanx; one of the conclusions drawn is that the pilum just wasn't that effective against the front of the phalanx - http://www.ancientbattles.com/WAB_Succe ... Legion.htm
PS - inasmuch as relative expense goes, not sure if there is any joy there. A Seleucid Silver Shield with light armour, shield, sarissa, an average statline and no special abilities is 16 points, while a Republican Roman hastatus with the same statline, same armour value (large shield), pilum, expert swordsman and maniple special abilities is 15 points (can be upgraded to drilled for +1 point). The Romans also have what appears to be an uncosted bonus of being able to operate under minimum unit strength without penalty.