The most commonly reported range on day one was 4-5k. But that means they didn't use all the free ones, which over course of the week is close to 1k in vlaue.

So assuming that you are ONLY getting the clothing and does not grow your tree aside from that, the expected cost is around 3-4k. There are a few reports of lower expenditure, I think I've heard of like 3.8k on day 1, so you could spend a bit less. At the same time, there are reports of spending more as well.

However, due to the way the tree works, the actual range can't be all that big. Because even if you get really lucky with coins, you are probably not going to complete it with 2k (+free rolls, for 160 or so rolls total), because you'd still be at a pretty low level tree at that point and thus completing it is doubly hard. At the same time, you can't really go too high because once you sank say 5k in (around 320 rolls), every other coin hit will net you a frag, so you really can't go that much beyond it. And given every roll grant a coin, there is literally a hard cap of 13k or so even if you never land on coins.