It depends on when you ask me.
If I've run out of products all together, my staples would cost me about $50('poo, condish, leave in, and gel). But the good thing is that I try to buy larger containers, so that they last me at least 3 months. I just recently ran out of shampoo (two weeks ago), that I purchased back in April. I think a 33.8 oz of shampoo that's used a least 2 times a week, lasting 5 months, is pretty darn good.
So, I guess this would be me at the "$25 or less a month" range.
There are occasions where I buy new stuff to experiment, but it still averages out to less than $25 a month(spread over 12 months).