Thanks, Ben! And I know exactly how you feel. That's more or less my situation right now.
I'm afraid I can't suggest anything from experience; I'm assuming Ben means you're from the US or the UK. I'm from India; the marketing, well, market, is quite different in our countries.
But I have heard that many authors (beginner authors) spend anywhere between $100 to $200 per month on reviews, podcasts, Instagram posts and ads, etc. just to get the word out. If you choose your services wisely, $200 can do a lot for you. But the question really is how much disposable income do you actually have. Even $10 can get you reviews and ads that can spread the word.
As for marketers, I think agencies dominate this field. Again, I can't recommend the Indian companies I know of, but I did find this article on marketing agencies in the US: https://writingtipsoasis.com/top-book-marketing-companies/
