aries — That is exactly what I am saying — you summed it up in one sentence.
real-brisker — Budgeting does not mean you are assuming nothing will change, and it doesn’t have to mean planning all your expenditures for the year. Some people budget monthly or even weekly. The idea of budgeting is that you live within your means by planning and keeping track of your spending. If Hashem gives you more you can then spend more — but to spend it in advance with the excuse that “Hashem will provide whatever I choose to spend” seems like bizarre reasoning to me.
Perhaps what is bothering you is the second part of your question “have almost every penny figured out”. Thinking that you have figured everything out does seem to indicate some lack of bitachon. I don’t think most responsible spenders believe they have “almost every penny figured out”. There are always unexpected expenses that come up, and there also may often be unexpected money received. If someone has a real unexpected need come up (medical treatment for example), there certainly is the concept of bitachon that you do what you can and trust that Hashem runs the world and whatever is happening is meant to be. If you are meant to loose all your money, all the responsible planning in the world won’t change it, and if you are meant to be rich the fact that you currently work at a $20,000 a year job won’t prevent it. That still does not give you the right to spend money you don’t have!
Again I’m not sure where budgeting sends the message that you believe the money is coming from a Basar V’Dam rather than Hashem. If you are uncomfortable budgeting in advance, work backwards — only spend money Hashem has already given you. So plan next month’s expenditures based on what you made this month, and if Hashem provides you with more next month, you can increase your budget for the month afterwards.
Would you say a person should just go out and buy the most expensive home on the market, and have bitachon that Hashem will give him the money to pay off the mortgage, even though there is no al pi derech hatevah way to get it? If anything I would say spending less or more cautiously is more indicative of bitachon, as you recognize that even though you have a current salary of “x” dollars, it is not in your control if that will continue, so how can you commit to payments in the future? No matter how good a moneymaker you think you are, Hashem is ultimately in charge of how much money you make. (I’m not saying that is correct, I’m just trying to logically follow your train of thought.)
From a mussar perspective it would seem lack of bitachon is more associated with having plenty and feeling that it is to your credit (“v’ram livavecha veshachachta as Hashem”), rather than not believing Hashem can give you more.