When I first started making pens, I bought lots of different style "component sets" from many different vendors. It was fun and I'm glad I did it. I got a chance to decide which styles were to my liking and what I didn't care for. As was said before, you get what you pay for. First let me say that I generally don't buy the gold plated sets. I stick with the titanium gold, platinum, rhodium, and black titanium. I also find chrome to be a nice wearing plating.
Once you get above the $10 to $15 dollar range for a set, you tend to get a metal finish that is better than the under $5 sets. Nothing big, but if you closely examine the metal parts by touch and with magnification, you find almost no rough spots or imperfections on the premium sets. These imperfections are not that unusual for a $3 slimline set. Once you get into the $20 and above range, the finish and quality of the metal parts tends to be perfect and the clips seem to be of a higher quality design. The ornamentation quality also improves.
Again, these are not make-it or break-it changes in quality. I doubt that the average customer would even notice the difference. It comes down to your own personal or business preference.