tip, hire a 'gofer' ...
A pre-teen can hand you stuff, and would be happy to get ~$5/hour cash. Eliminates the off-knees, on-knees pain (or down-ladder, up-ladder pain).
A teen might be trainable to mix batches of thinset (or prep in other ways), and would be happy at ~$10/hour.
An out-of-work...