your subject title refers to pricing design work but the met of the post seems to dwell on the actual physical labor.

Personally, I would price these quite separately. In my area, design work by a skilled professional is priced at $80-120 per hour, more if a name reputation. OTOH, labor is typically billed at $50 per hour per body.

But how you price is ultimately up to you, what you feel your value is and what your market will bear.

Dear Gardengal,
Thanks for the description of your experience pricing the work.
This is exactly what I needed to know.
I can scale my cost to my experience.
FYI I find that designing involves knowing soil conditions and what plants need, and finally putting desired plants in harmonious pattern...this is new to me but I always consider soil & sun first!