As some of the posts show, not only does a given boat''s budget vary widely from ''the pack'' but a cruising budget is actually a subset of a larger set of financial issues (re-entry costs, boat purchase/upgrade budget, emergency fund, etc., all funneling up to a total financial pot from which they all must be funded).
The best single source for coaching someone through all these issues...but tying them down to a specific boat and cruising plans...is in Beth Leonard''s Voyager''s Handbook (I may have that title off just a bit). Beth knows enough to correlate the financial planning issues with other directly relevant variables, e.g. the simplicity/complexity of the boat involved, and reading the chapter in her book is a big help in sorting out the micro and macro views.
FWIW Latitude 38 regularly carries articles on this topic, more often focusing on cruising on the W Coast of Central America but sometimes farther afield. While the details offered by their readers is always enlightening, their central theme carries right thru all the readers'' comments: you''ll spend what you have and, as a corollary, you''ll make what you have work if you''re committed to going.