What is "enough" though? 30%, 50%, 90%? And how much are we willing to spend to hit each of those targets. We're obviously not going to spend "infinite" economic resources to protect biodiversity and we've long since accepted that we are willing to sacrifice a bit of 'nature' for a bit of 'comfort' and that won't change. We're now negotiating how much we are willing to give up to save how much of nature, and that is, demonstrably, a very difficult problem.
I think it may be helpful to invert the framing of your question - you allude to spending economic resources to protect biodiversity, but aren't we actually talking about spending biodiversity (and other natural resources) to gain economic resources?
Your framing takes acquiring economic resources (a.k.a. the destruction of natural resources) for granted, assuming that we're losing, or giving up, something by opting to not destroy some portion of the natural environment for economic gain. Aren't we losing, or giving up, something every time we choose to gain economic resources by destroying part of the natural environment?
Logically, both framings are valid, but they don't appear wholly equivalent to me. Perhaps I'm missing something, but economic resources seem far more fungible than natural resources, which seems to imply that the latter framing may be more appropriate.
This difference, highlighted here, in this essentially ephemeral internet-space, may seem to occupy the border between semantic and pedantic, but I think it will take on a fundamental role in determining humanity's future prospects. How we define our relationship to the earth determines how we live. Your framing of the economic/environmental calculus seems to represent the status quo, but I don't think it represents a sustainable future for humanity. If/how/when the status quo shifts, I have no idea, but it does seem (from my limited vantage point, anyway) that more and more people are developing sympathy for the notion that modern society doesn't optimize for human well-being.
What is "enough" though? 30%, 50%, 90%? And how much are we willing to spend to hit each of those targets. We're obviously not going to spend "infinite" economic resources to protect biodiversity and we've long since accepted that we are willing to sacrifice a bit of 'nature' for a bit of 'comfort' and that won't change. We're now negotiating how much we are willing to give up to save how much of nature, and that is, demonstrably, a very difficult problem.