If you browse back a few pages on my comments, I've talked about the how-to at length. I may put some sort of e-book or long-form article together on this to lay it out better. In a nutshell, at the very bottom level you find people with a high appetite for risk who believe in the script and are willing to simply write a check. At slightly larger budget levels, you get access to some tax breaks or financial incentives, plus you can buy what's called a Completion bond that effectively insures the production to ensure the film gets made (subject to having a very very detailed plan and rock solid contracts in place). That costs about $100k minimum but ensures the picture will get completed. Beyond that you raise finance by getting presales agreements from distributors who put money in escrow or enter into sufficiently binding contracts that they can be used as collateral for a bank loan at an exorbitatnt rate of interest, in addition tot the completion bond. The massive risks involved are part of why Hollywood likes film franchises so much, because they make for more predictable revenue than one-off films.

It's somewhat the same problem with distributed patronage. It does work much better for episodic stuff as well as issue-driven documentaries and so on. But if you're limited to that approach then you're looking at no long-form stories, no historical fiction/fantasy/sci-fi and so forth, because of the up-front costs involved. Cameras and media storage are much cheaper than they used to be, but you still need things like lighting, props, locations, costumes and so on. The best prospect on teh horizon is Title III (equity) crowdfunding, where you are actually able to sell ownership units in the film rather than having to do a separate campaign of rewards/swag in return for donations. The Kickstarter/IndieGogog model has a lot going for it, but it strongly favors established rather than new properties.

The model for films today seems to be mostly driven by critic reviews, 2 minute trailers, and whatever all your friends are seeing at the cinema that weekend, which doesn't seem like a particularly good model either.

It's not so bad - people within the industry know how it works and there are established strategies for how to launch films of different budget levels. Bear in mind that the theatrical release is (except for the very largest films) basically just a marketing campaign for the DVD/streaming release. The fact of a film having played in theaters is an economic signal to consumers that it will provide a certain minimum level of technical quality.