How can I find the post on doing the grout for $2?

Diana, hope this is what you need: https://www.hometalk.com/diy/clean/bathroom/how-to-freshen-up-your-grout-lines-for-2-or-less--18698727

How to Freshen up Your Grout Lines (for $2 or Less)

Do you want to seal the grout?

'Painting' the grout lines with white nailpolish will give similar results to the painting with acyrlic paint, as shown in the photo above. Dollar stores usually sell nail polish for $2 or under. Nail polish, if applied correctly in thin coats, should not need sealant.

Quoting the $2 price for completing the project is deceiving though, as how far one bottle will go entirely depends on the sq footage you have to paint, how deep the lines are, and how much wastage there is in the process.

With nail polish, for the number of tiles shown in the picture, you will likely need several bottles, as the little brush on the wand will get gunked up, and the polish in the bottle with the lid off dries and hardens very quickly.

Hi Diana,

What is your project?

I would go with a paint specific for grout (or a masonry paint / sealer) to make sure it will last as long as possible.