Our local “Family Dollar Store” sells washcloths that are perfect as shop rags. The washcloths are sold in $5 bundles of 25 + 5 “free” as a bonus. That is 30 new terrycloth shop rags for just 17 cents each! The washcloths are located on the aisle with the bath towels (not with the kitchen or automotive items). They come in tan or light blue and are about a foot square in size.
A photo of these towels
This is the best deal for towels in the store, cheaper than their standard red shop rags in the automotive aisle.
These towels do a great job of wiping away bird droppings, cleaning brake dust off wheels, checking fluid levels, cleaning the engine bay, drying windows, and any other place you might use a towel or shop rag. But I wouldn’t throw out the nice detailing towels yet; these washcloths are very thin, very linty, and are of a very horrible quality.
Theoretically they can be washed and reused. I haven’t dared to stick them in the washing machine yet. Heck, at 17 cents, just soil the usefulness out of the rag and pitch it.
I have a sort of “cleanliness hierarchy” inside my mind. I use a new rag for drying the windows, then use it to clean bird poo and bug splat, then clean the wheels, then use it to soak up spilled fluids, finally throwing it in the trash. That doesn’t have to happen all in one day, I keep several piles in various states of soiled-ness and grab from the pile that I need.