Even if I don't try to dispute the idea that maintaining a minefield on the oceanfloor surrounded by a couple of big arse guns is more expensive than maintaining a fleet of 30 skyscraper sized robots (lol), my "boring" plan prevents the Kaiju from reaching and wreaking havoc with cities, which they routinely do with the Jager plan. How many billions of dollars of damage do you think they cause when they wreck a few skyscrapers and destroy a dock? The construction of a mobile strikeforce of mostly-conventional weapons in case Kaiju slip past the first line of defense is indeed possible and desireable, but instead of tiny fighters
going in for guns it should be a fleet of low cost bomb trucks like B52s dropping 4,000 lb guided munitions from low-to-medium altitude. Then you keep tactical, sub-kilotonne nuclear weapons on hand because we KNOW they work.
That's why I said
hassle, not talking about overall expenses which I believe are impossible to calculate. Of course, if we are going the realistic route there is no scenario in which making giant robots is a ever better idea, economics involved or not

I thought you meant big stationary weapon systems on the ocean floor, and the mines, and a big ass wall that could stop them before they reached the coast, all built miles beneath the sea level. If a kaiju comes out, and destroys these guns and defenses, rebuilding and resetting all those systems at that depth is as big a logistics nightmare as is lifting giant destroyed robots from the coast, that's all that I was getting at. I don't know how good we are at building giant deep sea structures, so maybe we need a kaiju attack to find out.
The whole idea (which they probably failed to convey) was that the kaiju were these sort of unstoppable forces that just kept going, and conventional warfare took too long to fell them and too much collateral damage, so it was absolutely needed to have something big that could stand in their way and grapple with them to stop them before reaching the cities (their primary target). I don't think the idea was to ever let them set foot on land obviously, and the ones we see slip by are after the Jaeger program is on shambles.
At this point I'm not sure what we are going back and forth about, but I take it you felt there could've been a better, more realistic plan of attack that involved the military parallel or prior to creating the giant robots, and the movie didn't satisfy your needs for that kind of leap of logic. I can see that, but I don't see the purpose of even going over them in this movie. I myself thought of big ass nets that could be deployed by submarines or planes to trap them and drag them around. I want to think the filmmakers made the effort to put all their eggs into the giant fights baskets and that's why they just glossed over anything else that wasn't that. I don't think all the things that were not considered inside the movie were out of neglect. If that broke your suspension of disbelief, well then that sucks =/
Detonating nukes over populated cities is one thing, and its understandible why people would object. But deep underwater explosions in the middle of nowhere in the pacific ocean? What's the objection exactly? Even if you just keep them as a couple of nuclear tipped torpedos as a last resort to prevent them escaping and destroying cities and shit, it's foolish not to have this stuff on hand. It's absolutely logical.
Deep water nuclear explosions do have an effect on Earth. Water moves you know, water cycle and all that. I don't know how many kaiju there were in total, but it had to be dozens, so that is dozens and dozens of nukes detonated to stop them. Sure, probably a better or more effective plan, but then we wouldn't have giant robots.