I was thinking less than $50.

I have been using a level.

For example, last week I was hanging some big 'ceiling clouds' 5' x 6' across and to make sure it was properly centered so I went through all the measuring on each corner up and down a ladder. Only after I was done did it occur to me that if I coulda projected a nice straight line across the ceiling, I coulda been done in a LOT less time.