I'm currently working on a startup in a different space, but one where my competitors often have similar scaling pricing. Every customer I talk to hates it. Interestingly, the problem most often cited is not that the scaled price is too high, but that it's difficult to predict. Paying $100/mo now and $1k/mo later isn't the problem - it's paying $100/mo now and paying some unknown large amount later. The uncertainty it introduces is the real problem, not the cost. I suspect you'll hear something similar - especially for a product whose main focus is financial planning.
That aside, this looks like a cool product! I feel like every tiny startup I've worked at has had some flavor of this problem and solved it with ad-hoc spreadsheets. Seems like a solid niche. :)