You pay half for a bonus.  Asteroid mines add a flat value rather than a percentage, so they don't count-you pay full for them.

This means if I have, say, 40 industry on a planet, with a 60% military bonus (and assuming I'm running at 100% funding and 100% military), I get 40*1.6=64 military out of it, and I pay 40 + 40*0.6*0.5 (60% bonus and 50% for what we pay) or 52bc for it.

It gets a little more complicated if you involve focus, due to how bonuses are treated, and there's some weird bug with regards to the Artificial Slave Center, but overall, that's how it works.

As for a free lunch...this is not the free lunch you're looking for.

No, really.

I don't know all the race techs. For economy there is a traders den in the korath tech tree. Knowing this I can believe there is one for industry. The krynn have high approval especially with norale maxed out and a populists party with maxed economy. it helps to have a maxed out population. ps. worry about entertainmemt it pays off. In the endgame this is not inportant. I would not recommend this but if you don't build structures, you will probably play in the green, or you could not build ships on every planet. Thalans and the Yor start with bonuses. You will temporaly, probably. eventually have to lower production in the civilization screen. Adding to what I would not recommend, you could cut research in the civilization screen for production. Economy and approval is more inportant than production. Build market places as you build factories is your best bet.