This paper explores the potential of Fused Deposition Modelling (FDM) three-dimensional (3D) printing for the cost-effective production of metallic-type antennas, particularly horn antennas aiming at K-band. The focus is on the electromagnetic (EM) performance of two 3D printable metallic materials: BASF - ltrafuse 316L; and Formfutura - MetalFil Classic Copper. Simulations were conducted on horn antennas at 18 to 26.5 GHz, revealing that the total efficiency of the 3D printed antennas decreases almost linearly with the increase in surface roughness, impacting on the overall performance. The MetalFil Classic Copper antenna exhibits a more pronounced decrease in efficiency due to its lower electrical conductivity and increased surface roughness. The study highlights substantial cost savings with FDM printing compared to traditional manufacturing methods, e.g., metal milling, with the Ultrafuse antenna being approximately 10 times cheaper and the MetalFil antenna around 100 times cheaper than their traditional counterparts. Consequently, 3D printing is sought to be a viable solution for fast prototyping while yielding similar EM radiation efficiency compared to that of traditional milling (subtracting) techniques.