It can only be bought for robots and it has a huge chance of failure. I think its cheapness is okay. Maybe if you want more detailed rules, it could be such that for every inch in size it costs 2 cp so a 3" death robot would have to spend 6 cp to get it since it's bigger. Or something like this:

Level Cost:

2 cp per chance on a D6...

6 only = 2 cp

5 and 6 = 4 cp

etc, but max is 4 5 and 6

Then multiply that by the size in inches.