Yours is a loaded question, as who knows how much you have to spend. The cheapest route is Zimbabwe to hunt only kudu and buff. I don't know if you can hunt kudu on the cheap "buff-only" hunts in Tanz.

I would budget in US dollars, for Zim:

Passport: $?
Visa: $30 for Zim and no need to get it early, but this varies in cost and should allow lots of time for sending the passport to the embassy of some countries to get the Visa before your departure.
Plane from US departure city: $2300
If you charter into camp: $1500 (depends, but the sky is the limit on charters! Depending where you hunt, you might also be able to drive in. You can also split the cost if someone goes with you).
7-day Buff hunt & trophy fee: $7000
Kudu trophy fee: $800
Tips: $800
Dipping and packing: $400 (This is pretty much an arbitrary number and negotiable in many cases).
Shipping and expediting of trophies: $1800

That's most of it. Gets expensive, eh? Better to budget on the high side. You can always bring home leftover travellers checks!

You need to talk to several references (names and phone numbers) of ANY outfitter/PH. Things rarely stay the same even from year to year...guys go out of business, loose concessions, get killed by buffalo, fly off to Hawaii with a clients wife, etc.

You can reasonably expect a 36" or better buff and a 50 something inch kudu. Only the big ones wind up in the ad photos!

You need to get yourself to an SCI meeting! But don't get caught up in the excitement without talking to someone that has been there and done that.