Mine costed 0, i simply bought every day medium threads from monthly event and spacetime shop. I was also lucky because i leveled it up at 72/100. But in average you level it up at around 90-95/100 that are 450-475 medium threads.

Unless my math is incorrect, it would cost 17,100 coupons/ ingots if you purchased them from the shop (assuming 450 threads purchased). Of course, it would be better for you to claim them from the monthly event or any weekly events as much as you can as it can be very expensive (over 300$).