Hump, Nishimura, Tsukiji, Tsukasa
The cost of omakase depends on the number of servings and the cost of the ingredients. Certain ingredients, like abalone and uni, are more expensive than ingredients like tuna or red snapper. I think it's best, therefore, to talk about relative ranges of prices. I usually order quasi-omakase, meaning that I am guided by the chef's recommendations, but also specify certain items that I'd like to have if available. Needless to say, when you've established a relationship with a sushi chef, he knows what you like from his memory of your previous orders, and tries to anticipate your desires.
Nishimura is the most expensive option. It is a physically beautiful restaurant, tastefully elegant, but with limited options for types of sushi and sashimi as compared with, say, Tsukiji or Tsukasa. On a recent visit to Nishimura, my wife and I had hamachi sashimi, red snapper sashimi, albacore sashimi, maguro sushi (two pieces), otoro sushi (two pieces), marinated mackeral sushi (two pieces), kohada sushi (two pieces), snails (baigai), ama-ebi sushi, anago sushi (two pieces), a crab handroll, a cod roe handroll, and uni sushi (four pieces). We asked for ankimo, engawa, and shirako, but none of these was available. By the time we finished, we had pretty much exhausted the selection. Cost, with one large Sapporo and one small Ebisu, tax and tip, was $166. A similar meal for two at Tsukasa or Tsukiji would be closer to $100 for two. It's been a while since I've been to The Hump (Nishimura used to be the sushi chef at The Hump before opening his own restaurant), but the prices are also generally higher than Tsukasa and Tsukiji, and closer to those of Nishimura. There is also a difference in clientele. Nishimura and The Hump have a largely non-Japanese clientele. Tsukiji, and especially Tsukasa, have a primarily Japanese clientele.
Tsukasa is the most traditional of the sushi restaurants you mentioned. Tsukiji is more in the "New Tokyo" vein, with some experimentation in saucing and flavoring. Nishimura is also in the more experimental vein. For example, on our recent visit to Nishimura, the hamachi sashimi was served with finely sliced serrano chile, a leaf of cilatro, and a small dab of garlic. It was delicious. On the other hand, the red snapper sashimi was served with a garlic chip that overpowered the delicate flavor of the snapper, although the idea of the crunchy texture of the garlic against the soft texture of the fish was a good idea. The Hump is likewise in the "new sushi" camp. Nishimura and The Hump clearly reflect the experimental influence of Nobu Matsuhisa, whose restaurant is yet another choice you might consider if you are interested in non-traditional sushi.
re: Tom Armitage
I had the omakase at Tsukasa in Little Tokyo several months ago. I may have mentioned it once or twice before on previous posts.
Now I really wish I was taking notes as I was eating, but I'm sure that would of been rude. Among the things we had was the standard sashimi pieces, scallop sashimi, a few baked (or broied) items, uni, no exotic stuff like monkfish liver, and sake chosen by the chef. It cost us $65 a person.