Had the same exact issue when my starter failed on my gen 4 zx10r.
You can supply direct power to the starter with a pair of jumper cables and a screwdriver to eliminate the harness(relays, switches, etc.) as a culprit. You are gonna have to tear it down pretty far for to get a decent amount of room to work around by the starter. If you feel you are nimble enough you may be able to just remove the coolant line, thermostat housing, etc. and snake the power in there. I am hearing more and more cases of gen 4 starter failures so my money is on the starter, but diagnose before you start replacing.
Depending on what went wrong in the starter there are some places that can rebuild starters for a good deal less then $400, if interested I can send you the shops information.
The more you learn, the more you realize how little you know.