As you said you don't have money and you don't want to do guest posting to increase website rank on google. I suggest you to make your website content attractive and you can optimize website too. Regards TrustLogics

Definitely blog commenting help in generating back links just you need to follow some rules.

1. Check DA & PA and compare with your website
2. Check previous comments is that blog giving do-follow or no-follow back links.
3. Finally write appropriate comment to matching your niche and blog niche with links in it.