I do not believe that one can make a blanket statement that one process is always lower in cost than another process. One would have to look at the application.
In general, the cost is dictated by the labour costs rather than the consumables, although it obviously also plays a part. In the case of FCAW, the deposition rates are generally higher. If you can take advantage of these higher deposition rates, then this process may be less expensive.
On the other hand, with GMAW you have much less cleaning. (no slag) If you can take advantage of this, then GMAW may be the cheaper process.
Done properly, FCAW should give as good a result as GMAW.
Regards
Niekie Jooste
As Niekie has stated it is hard to give the right answer to suit your needs. However, if you like the easy to clean aspects of GMAW and you want the penetration of FCAW perhaps you should examine metal-core arc welding. It is a compromise between the two processes.
Your local welding supplier or welding engineer will be able to help you pick out a process that is best for you.
Regards,
Sean