Fun fact

3 frags on normal at 10 SoT per run

4 frags on hard at 15 SoT per run

5 frags on madness at 20 SoT per run.

It's actually cheaper and more conservative to play normal mode and save ironite. Takes 250 normal runs to get him and there's 20 possible keys to get, and 15 runs per key times 20 is 300 runs so you can do the whole thing on normal for about 630ish ironite.