Hi-Value Mines is an upgrade in the Support Monkey Knowledge Tree that was first introduced intial release. It allows the Spiked Mines upgrade to cost $1500 less regardless of game modes. Hi-Value Mines requires Very Shreddy before unlocking this upgrade, as well as 8 Knowledge Points purchased into the Magic MK Tree before being able to be purchased. There is a one-off purchase of 500 before unlocking for the first time.
The following are prices for the Spiked Mines upgrade with and without the effect of Hi-Value Mines: