Breast feeding

So our plan to only breast feed was thrown out the window approximately 2 days after Eli was born because he wouldn't eat and wasn't latching on...fine, no big deal. Here we are 3 1/2 weeks later and I'm still not making enough milk. Since he was 1 week old and not gaining weight we have had to supplement formula, but now he's starting to eat more and I'm barely producing an ounce every time. I know it's best for him so I'm ok with giving him formula, I'm just a little bummed it didn't work out. Also formula is crazy expensive! Are you ladies breastfeeding? How's it going if so?