How does the tinker cost reduction work at Science 100?  I'm maxed out with tinker costs at 16k for some weapons.

Tinkering costs always start out at the lowest cost for any weapon regardless of the level it is when you get it, so you're probably better swapping off swapping out for a weapon with a higher base level at some point, and leveling that one up. Unless you've got a unique you really like, I suppose.

Science does cap the cost of tinkering with science weapons to 200, regardless of level.