Homi had a good thought about button placement, where we could actually place the buttons on the side of the blocks and not worry about needing to remove buttons to replace the ice. Here is a screenshot in my testy world of testfulness showing the correct and incorrect placement, the correct is marked by a green banner and the incorrect marked by a red banner. Please note the button colors are only to allow clarity, and are not an exact copy of the tunnel.
Forseth also had a good thought, this one pertaining to blue ice placement. To severely cut back on cost we could ice intermittently, replacing some ice with a layer of slabs. Again I have provided a screenshot from my testy world of testfulness detailing the high, medium, and lowest cost layouts of blue ice, marked by banners. The highest cost is marked by red, middle cost is marked with yellow, and lowest cost is marked by green. Please note the blocks in these pictures are to allow clarity, and are not an exact copy of the tunnel.
I would also like to mention we are drifting into that classic LVS council territory where one topic becomes two, and two becomes four... It may be best to let the ice-change topic rest while we talk about the buttons, with the knowledge from my first screenshot and explanation that Homi provided.