How to word this equip reduction ability?

I am working on a homebrew card and this ability I want to make sounds incredibly awkward, so I'm hoping there's some better way to phrase it. Any suggestions would be appreciated.

"Equip abilities targeting [this card] cost X less to activate, where X is the highest mana cost among the equip abilities of equipment already attached to [this card]."

The intended effect would play out like so:

1. [Card] is on the battlefield, without equipment.
2. First equipment, [[Skullclamp]], costs 1 and is unchanged.
3. Anything with a normal equip cost of 1, such as [[Adventuring Gear]] or [[Champion's Helm]], would be be free, but wouldn't reduce the cost of any additional equipment.
4. Second equipment, [[Grafted Exoskeleton]], costs 2 so its cost is reduced to 1. Now anything like [[Basilisk Collar]] that normally costs 2 would be free.
5. Third equipment, something like [[Baseball Bat]] that normally costs 3, would only cost 1. The total amount of mana that would have been spent on equipment abilities would be 3 at this point.
6. This trend continues; something like [[Grappling Hook]] is reduced from 4 to 1. But if you'd started by equipping Grappling Hook for 4, then all of the others would have been free.