We may have discussed this topic before.
I pay $40 for a term (About 2.5 months) here at Carleton. I don't remember how much I pay back home.
There's also a $30 annual fee. (Organizational)
Kyu tests are on an ascending price scale. Not that expensive; my most recent test (5th kyu of 9) was $25.
(Kyu tests are also organizational expenses.)
In terms of the more philosophical assessment, Aikido is definitely an expense. It's something I make room for in my budget. Some of my friends buy lots of anime, or have some other expensive habit. It's a choice in that regard. I think it's money well-spent, to help support the organization and dojo that enable me to study aikido in this way.
And like, I imagine, nearly all dojos (as those which have been mentioned above), we don't turn anyone away for lack of money.
A 'clinic' weekend (like a 'seminar' or what-have-you) can run about $150 if you do everything; typically 4 hour or so intensive clinics and a regular class or two while we're there.