What are other purchasing costs. Is HST a cost?

Is your question related to inventory? If so, is it for merchandise purchased for resale or raw materials purchased for use in a building or manufacturing process? Or, is it for finished, manufactured, or constructed goods?

Yes it is related to merchandise purchased  (work books used for teaching) each participant receives one. I am not big enough to have an HST number

Still need a bit more specific information. Are these books you purchased for your own use? Or, do you buy books to give to your students who take your courses/training?

They are books to give to the students for their use and they keep them

Since you are not an HST registrant, you can include the HST with the purchase price of the materials as a business expense. 

Thank you