Well the original Kamino clones yes those are not very cost effective. However, they did serve their purpose which was to be completely loyal to the 'Republic' even so far as taking orders without question, hence Order 66. In that perspective the clones were needed since ordinary recruits would have hesitated or balked at the idea of killing their Jedi commanders. Supposedly over time not just Kamino produced clones but other worlds as well obviously. The spaarti method is probably used which reduces growing the clones to mere months if not only 1 year. The advantage to using the clones is more than just say cost effectiveness but loyalty. The clones will be obey any and all orders they get. Recruits, not quite the same. Thrawn's method is infinitely better since he was able to grow clones in weeks...imagine churning out pilots and soldiers in a matter of weeks with full training and knowledge of tactics. If that were the case then clones would be superior since it takes a while to train recruits. Also, with the clones one can use certain traits which are suitable for the environment and genetically engineer them specifically for their role. For instance the clones in the Clone Wars there are pilot clones and soldiers etc. The pilot clones are in general shorter than their soldier peers and possess faster reflexes which makes sense. The soldiers on the other hand tend to be slightly bigger and have less independent thinking. Also, in terms of cost now manufacturers can standardize the gear that is produced. From an economic standpoint that is fantastic because now you dont have to produce several different versions of one item due to physical variation. I think some people quickly dismiss the advantage of clones when it comes to cost effectiveness and forget about other economic factors.