Theoretically, if your rods are not hardened, the balls in the bearing will scratch the surface very quickly. So, be sure that they are stainless steel, hardened and with h6 tolerance. I asked some companies (I wanted to make them by myself, too), but they told me prices like 40-45$ for a linear meter which was too high for my project. I bought them ready made on the Internet.
Best regards,
Bobby
