I'm a r4 tailor on Mari. If someone provides the materials and pattern, I work on tips. If I provide the materials, I use high-end material costs for the estimate, while buying low/making materials.
My two cents: I have never made a vito-crux, and would flip just to have the opportunity to put my name on one (let alone 4). This is probably what is motivating Juno's offer to help.
Depending on how close to ranking your friend is, he may be spending 1-2 million (I dont know prices on your server-- so numbers based on mari) just to have the opportunity to help you. While you could go to a tailor that is a higher rank, your friend is willing to grind tailoring to help you. That says a lot, and shouldn't be overlooked when deciding if this is a good deal for you.
The part that is confusing me though-- you are acting as if you have to have enough materials to use the entire pattern all at once. I'd let your friend rank to r6, while collecting enough materials to finish one (or more) Vitos. Have him make a vito, sell it, and use the proceeds to buy the rest of the materials.