There is no shortage of people who will take your money if you're a writer and think you need to pay for help. I can remember buying Writer's Digest magazine years ago. Mostly it just added to my recycle pile. I'm not saying there's nothing there of value, but it was of no use to me at that time. Maybe now I would find more in it that would be useful, but I don't want a magazine subscription anymore.
There's probably several forests worth of how-to books on writing. I've spent a grand total of twenty dollars on such: Stephen King's On Writing and Strunk and White's Elements of Style. There may be a few other good ones out there but I think this is a real "buyer beware" area. I'm not the biggest fan of self-help books and I think there is a very fine line between self-help books and many of the writing how-to books that are out there. The very best money you can spend on books that will help you learn the craft of writing is on fiction. Read a lot, read widely, read, read, read. In your genre, out of your genre, just read. It will do more for your writing than any how-to on the market.
There are plenty of websites that claim they can help you with networking and publicity for a nominal fee. Maybe they work, I really don't know. It would be interesting to hear from someone who has used those pay sites and find out if it helped their sales. To be honest, I don't have the disposable income to afford a bunch of memberships. As a reader, I rely more on review blogs to learn about new books, but maybe other readers do look at these sites. It does kind of seem like they are more or less marketing to other authors, which is something you can do for free on your own in various ways. But again, I don't know. Just because I don't use these sites as a reader doesn't mean other readers don't.
There are organizations you can join, too. From what I can tell most of the big ones require you to have a deal with a traditional publisher, in which case you can probably afford the organization's membership fees. I do think it would be worth it to join the Romance Writer's of America (the RWA does not require you to already have a traditional contract, but be serious in pursuing a career in writing romance and it's sub-genres.) There's a chapter in Nashville where I could attend meetings. Two things hold me back: money (as always) and the fact that I still write mostly urban fantasy. I do find myself edging into paranormal romance territory more and more often, though, so it would probably be okay for me to join the RWA.
There is an organization for writers in digital publishing, called EPIC. I haven't joined it because of a) money and b) I don't know why. I think I feel like I'm still too new at this to think of myself as being remotely professional. To be honest, I'm not very good at the business side of writing. I try, but I don't think I'm doing a very good job at that side of things. I may join EPIC next year but I'm not sure.
In my opinion there's only two things you absolutely have to spend money on: the filing fee for your copyright, and that's only after you get the final copy of your work from your publisher, and a domain. I spent ten dollars to turn my personal blog into my own domain. I went that route because I don't know how to code or design a website but I do know how to work Blogger.
People will tell you that you have to do this, that, and the other in order to "build your platform" or "advance your career" or whatever phrase they want to use. When what they are telling you involves you, the writer, spending a lot of your own money it's either because they want you to buy their service or they have plenty of money of their own to spend. Money can be a very touchy subject. Aspiring writers often don't like to hear that if they're in this because they want homes in three states like John Grisham, they might as well give that dream up. Very, very few writers make anywhere near that kind of money. If I ever get to the point where I make the equivalent of minimum wage from my writing, that will feel like a major accomplishment. I have to take that into account when I consider how much money to spend on my "career" - how much of a return on investment am I likely to see? I spent way too much money on promotional book cover cards that very few people wanted - lesson learned. It always pays to think through your promotional investments. If your book will be digital-only, why are you considering promotional bookmarks? Maybe business cards would be a better idea.
There's a lot to think about when it comes to handling the financial side of your writing career. This post just scratched the surface, with no mention of business licenses and taxes, or working within US publishing from another country. The most important thing you can do is homework - find out as much as you can before spending any money. And think things through. Imagine this scenario: you're in a bookstore, you've got twenty dollars burning a hole in your pocket, and there are two books that have drawn your attention. One is a how-to, with some crazy title like Write That Novel In a Flash! (Exclamation point included.) The other is the newest release by an author who never fails to drag you into their fictional world. Think about which one you're more likely to learn from about the art and craft of writing.
With any luck that novel is a paperback and you can afford a cup of coffee, too.