I baste for my friends all the time. They give me about $35 to $45 per quilt when it is twin or double. I use a light thread and put a line across the quilt side to side about every one to one and a half feet. It usually doesn't take too long but it helps them out a lot.
Once I even turned it and put lines in a grid all through the quilt so she could travel in the car with it, it was less than twin sized. Good Luck and enjoy.