Niobium-coated copper cavities are an attractive solution for RF superconducting structures. The copper parts are usually obtained by spinning and subsequent weldings. However, the defects of welded surfaces may create local coating problems. One way to minimize them is to hydroform monolithic cavities starting from OFHC (oxygen-free high-conductivity) copper tubes. Manufacturing procedures are presented. The very encouraging results obtained on multicell pieces for frequencies of 2.1 GHz and 1.5 GHz are correlated with theoretical computations. Extrapolation to the hundreds of megahertz frequency range is discussed from the technical and financial points of view. On the technical side, the main advantages of hydroforming over the present manufacturing technique are the suppression of the critical welds, a better geometrical accuracy, and better thickness repartition. On the financial side, the proposed fabrication is easier and shorter per cavity and the large initial investment is quickly amortized even in the case of a small series production. >