We propose a magnet featuring a standard 52 mm bore that creates a longitudinal magnetic field. The magnet is made out of commercial magnetized NdFeB cubes, costing less than 100 €. This device is a low-cost solution to build a portable magnet generating a field of 100 mT with an intrinsic homogeneity as good as 40 ppm over a 5 mm3 volume. Furthermore, the bore can accomodate a standard narrow bore shim stack and NMR probe in order to shim the field and conduct low-field NMR experiments. We established an assembly process including characterization of the magnetic cubes, cube sorting and optimization of the assembly according to the needs of the application. Aspects of the assembly method are discussed, including characterizing the magnet cubes, sorting them and arranging them in an optimal fashion.