Also in one of the niches, I have a competitor who is 3 months old ( like my site ) and is already in the top 10. The difference between our sites is that he has 60 links, DR 40-80, mostly guest posts, and I have almost no links.
you've just answered the question in your title with this statement

... Well, the 1st part of the question anyway...
For the 2nd part (where to get links), here's a guide I've written a few days ago in response to someone else:
https://www.blackhatworld.com/seo/w...ink-from-for-my-website.1646195/post-18297106
How much should quality links cost?
quality links can be free too, they don't have to cost anything if you know where and how to get them. Someone shared a case study on the forum last year I believe, in which he showed how he ranked a fresh website (in Health & Medical niche nonetheless, which is brutally hard to get into) with only forum links. And while it's possible that he didn't get those links for free (he probably used a paid software to inject the links into the forum posts), those links can definitely be gotten for free if you're active on those forums and gain enough privileges to be allowed to post links...
And that's only 1 type of links (specialty forums) that are free and quality enough to rank. Other types of links I can think of are .edu / .gov links. These can be gotten for free too if you have the right tools / connections...
And there are almost certainly other links that can be obtained for free and that can be considered quality depending on your goals, but I'm not going into details on all of them (partly because I don't remember them all

but also because it would take me a lot of time to explain how they can be valuable, but I'm thinking of Pinterest, Reddit, PDF submissions, and podcast links here mostly, these are usually free and can help you rank in certain scenarios)
So yeah, you can get links for free for sure. But you can also get links for extremely high prices. Someone had shared a free pdf on the forum a while back (1-2 years ago I think) of a SEO agency that was charging $30k for a link from Cosmopolitan, which seemed crazy to me but hey, not everyone's poor like me
But anyway, the point is that backlinks can cost anywhere from $0 to $1000s, it depends on who sells what links. So, it's hard to answer your question...
Most of the sellers that sell link packages for $50-$100 have a huge number of positive reviews
I find that suspicious, too. But I'm not speaking against it because I don't want to risk getting banned or argued with by higher-uppers
This being said, the links have the power and purpose that you give them. If you buy "web 2.0 + profile link" bundles and expect to rank for "weight loss" or "buy smart TV" (no matter if those links cost $5 or $500) you're in for a shock.
Most newbies think that they pay for links and the sellers will rank them outright. If SEO was (still) this straightforward I would still be in it today. But, unfortunately, it's become the game of the rich and the geeks, people like you and me (or maybe like me only, I obviously don't know you), can not compete with entities with millions of $$$ monthly budget for SEO alone, or with born geeks, programmers and hackers. Sadly, this is the environment we live in, and backlinks have very little to do with it. You can rank even without backlinks if you know what you're doing (albeit I suspect that you'll only rank for a short while, until a smartass or truly dedicated person finds your niche and builds links to their site to outrank you)... or with any type of backlink if you know what you're doing. So like I said, the backlinks have the power and purpose that you give them, although there's no denying that there are quality backlinks out there that can move the needle in any niche. But those links can be expensive as fuck as I just mentioned earlier (upwards of $5000 a pop)