is a good deal to buy the ocs for 180 or buy the units individualy

Depends on how much you can get it for and whether you want both sides or not. All you need to do is work out the individual costs you can buy them for and compare to the price of the set taking into account all the other extra's like terrain boards and dice.

it seem for units is almost same price but without terrain and dice. i cant find any lower than 180 dollars

i got sniper, command squad and 2 medium walkers for each side im happy now for 100 dollars