I met this gentleman at GenCon during a steampunk event. Like me, he is an avid shopper at thrift stores. It's possible this comes almost entirely from thrift purchases, although I can't remember that for a fact.
The pieces of this costume work well together yet avoid the trap of over-dependance on neutrals. Instead, everything is organized around blues and purples, and with the exception of the tie, everything is fairly muted in tone. Moreover, shirt, vest and pants all have vertical stripes, creating interest without conflicting patterns. The hat could have easily been acquired plain and then had the band added for decoration as well as uniting it with teh rest of the outfit.
Victorian men often wore their pants closely tailored to the leg. You're not going to find a lot of pants like that in the men's section. You're even less likely to find a striped pair. These were purchased from the women's section of a thrift store, which is the most likely place to find them.
There's not a lot here that screams steampunk, which is absolutely fine. He has, however, added a few notions to the left side of the vest. It's a nice touch that separates the costume from just being a period piece.
The screaming red lanyard probably holds his badge for the convention. It's not part of the costume.