Welcome to the addiction!
Honestly, the Ultimate Kit would be the 1st choice since you'll just end up getting it all anyway . I do understand the cost may be prohibitive, but with it currently on sale plus an additional 18% off, it's hard to beat!
Otherwise, I've always been partial to the Winter Wash Kit. Don't let the name fool you, it's good for all year round. Then, you can add a Clay Bar kit and one of the polishing kits of your choice and you'll be pretty well off to start.
Whatever you get, agreed with Nick...definitely take advantage of the 18% off sale. FYI, 20% is about as good as I've seen offered at any point in the year.