Actually, if you want a discount you'll do more than that.

[Tohsaka latches onto that curiosity of his as he draws in toward her work. She's always been a bit of a teacher. For Shirou, for Atsumu... she can't help it! She likes flaunting her knowledge, but also to see people grow and gain experience. She likes watching people try hard, and get rewarded for it.

Rin presents him with a mortar and pestle before pushing a bunch of ingredients his way.]

I will leave you with instructions while I go procure a brush. Do you think you can handle a little hard labor?

[Hardly labor - unless you count the meticulous grind of herbs into a fine powder.]