The cost of terraforming Venus would be large, but the benefits of having a second habitable planet are also quite large. Even ignoring the benefits of having more land and resources, there's also the just the fact that being on two planets means we can potentially survive as a species if something happens to one of them.

It would also have to be heavily automated, and only really becomes realistic once you have machines that are essentially self-sufficient at which point the concept of "cost" becomes a lot fuzzier. It would mean dedicating resources, but you aren't paying an army of self-replicating robots.

However, the sheer scale of the task means that the benefits would only be seen many generations later. It would require extreme efficiency and long term planning with little tolerance for error. The kind of people who would make such an investment are unlikely to just hand the money over to the shadiest billionaire they can find. And it would be difficult to keep a scam going if they need to show continual progress decade after decade.

Maybe we'll never see enough progress to overcome the kind of greed and short term thinking that would doom a huge, world-altering endeavor like this. But if that's the case, it's more likely that we'd just never try. All the more reason to keep pointing out what could be instead of just accepting the shittiness that we see today.