I did it like this a few years ago: I ordered the metal parts from one of the online railing shops (for me: stainless steel from Cosch, full recommendation). There you can immediately see the prices and get a feel for material costs. They also provided good advice over the phone. Then I ordered the glass cut to size from a glazier, with the necessary drillings. For this, I simply prepared a tender and emailed it to various glaziers, the contacts I searched for online (e.g., eBay). Overall, this was much cheaper than comparable complete offers I found.
Warning: there are big differences in glass. Back then, for example, many eBay complete railing offers were certainly not suitable as fall protection (too thin). For me, it became laminated safety glass made from heat-strengthened glass, as a compromise between residual fall protection after glass breakage (possibly problematic with laminated safety glass made from tempered glass) and lower probability of glass breakage (compared to laminated safety glass made from mirror glass). Also consider the possible glass properties. Thicker glass looks slightly greenish, for example, whereas there is "purer" special glass.