UPDATE: Equipment Upgrade Cost Chart
I have compiled what I could... but am missing some info.. can someone add valid info.
1-2 5k 2 coins
2-3 7k 3 coins
3-4 9k 4 coins
4-5 12k 5 coins
5-6 17k 7 coins
6-7 22k 9 coins
7-8 30k 12 coins
8-9 41k 15 coins
9-10
10-11 74k 21 coins
11-12 101k 25 coins
12-13
13-14
14-15
15-16 334k 48 coins
16-17
17-18
18-19
19-20