You do not buy a high level stone ready-made: it climbs by merging. You put together two stones of the same type and the same level, pay the gold fee, and out comes one stone of the next level. Then repeat: two level 2 stones become one level 3, and so on to the top.
The attempt can fail — but the risk is only to your wallet: if it fails you lose only the gold, and both stones stay with you. You can try again right away.
| Merge |
Cost |
Success |
Failure |
| Level 1 + level 1 → level 2 |
5kk |
96% |
4% |
| Level 2 + level 2 → level 3 |
10kk |
92% |
8% |
| Level 3 + level 3 → level 4 |
20kk |
88% |
12% |
| Level 4 + level 4 → level 5 |
40kk |
84% |
16% |
| Level 5 + level 5 → level 6 |
80kk |
80% |
20% |
| Level 6 + level 6 → level 7 |
160kk |
76% |
24% |
| Level 7 + level 7 → level 8 |
320kk |
72% |
28% |
| Level 8 + level 8 → level 9 |
640kk |
66% |
34% |
| Level 9 + level 9 → level 10 |
1,28kkk |
60% |
40% |
Look at the maths: reaching one level 10 stone takes 512 level 1 stones, and the fee doubles at every step. That is why level 10 is rare, and why it pays to start collecting bags early.