Absolutely no treatment. Choose a grout color that is dark enough. I have spilled motor oil on the grout many time.... Once cleaned with a rag you cannot tell.
This floor is abused heavily. During winter time my wife's car is in. And because of the harsh winter, the floor is always full of mod, salt stones..... and if that is not enough she have studded winter tyres.... Once in a while rinse with a hose and thats it
Yes less than a buck including grout and glue..... I did it myself... I paid the tile 0.65 cents each 12.5 X 12.5 inches.... watch leftover/end of line sales.
This is an example:
https://www.homedepot.com/p/Daltile-Catalina-Canyon-Noce-12-in-x-12-in-Porcelain-Floor-and-Wall-Tile-15-sq-ft-case-LV021212HD1P6/203233529
If you shop around, you'll certainly find the right color.
Again choose a commercial grade porcelain.