Actually Spartans wouldn't be that expensive. I don't think they would cost too much over 10 CP, unless you count the weapons. Those specialties seem pretty cheap, when you compare them to the costs of Ninjas specialties. So they cost less than a Ninja, unless you make them even better CC figher.
And if you don't have enough pieces to make a full squad of decent Spartans, they don't have to look exactly like real Spartans. If you ask me, I'd just give everyone a Spartan-looking helmet and a spear and that would do. Other than that, it's free. We have parts for only one or two 300 style Spartans, but for a full squad of armored Spartans.
In fact, we have two Spartans in our future game. They are really only Ninjas with no stealth and fudged 'Spartan' ego, but they look Spartans. One has armory, and the other is 300 styled. I'll take pictures of them, and upload them on Brickshelf. But you'll have to wait, I'll get the pictures on the web at the same time with the battle report.