If you think it's a good idea to buy Instagram followers, I want to tell you that no it's not.
Buying Instagram followers is a short term gain which will negatively effect your account in the future because the Instagram followers you are buying will be bots, and they will not engage with your posts ever. They are low value accounts probably following thousands of others and have miniscule followers themselves.
Instagram realizes what is happening and sees your audience as low value, they see that your followers are not engaging with your content and they assume your content is shit.
This is not what you want for your account, you don't want to take the easy route and buy a bunch of followers for cheap if you plan on anything long-term with the account.
I suspect most of these services are bought by con-men who are attempting to perpetuate an image of success so that they can sell the Instagram account to some poor sucker?
Is incredibly important, it signals to Instagram that your account is valuable and that your content should be promoted more often to your followers. Instagram only wants to show the best content to it's users so that they have a "better experience".
You may think that buying 1000 followers for $5 is a good investment. And yeah that price is pretty good, not going to lie. It will make you feel good to see these new followers coming in, even though you may know that they are fake accounts yourself. It will feel good to be seemingly more popular than you are.
But this is going to have detrimental effects to your account in the long-run, making it entirely useless. If you are going to invest in your account in the first place, purchasing things to improve it, there is no point in doing this. Because you are just shooting yourself in the foot for small quick gain.
You are being lazy and stupid as a matter of fact.
What you could do instead is invest $15 dollars and pay an Influencer for a shoutout, now you may only get 30 followers from something like that, but they will be real people and they will actually give a shit about your product.