Giving Products as Tithes

I wanted to know if I, as a scribe, can give my mezuzah as tithes, for the fixed price at which I sell is to the dealer. (It should be noted that he buys everything I write) And if so, should this be considered less than tithes? For example, if I sell to a dealer for 500, then I separate tithes from it, pay national insurance and so on, leaving almost 400 in the end. So when I give, should I calculate as if it's 400 or as if I gave 500?

Dear …!
It is permitted to give a product to charity, and to count its full value as a tithe.