From your OP:
prices naturally come down as manufacturers try to cut costs and maximize profits
Now you say that manufacturing doesn't bring down prices?
We should be waiting until solar panels are the best alternative before mass production
So as soon as it's cheap, it's good? News flash, it will never be cheap and it will always be getting better. You can't wait until its 'better'. If you wait, you never start. Solar power is fully realizable right now, there are simply no technological hurdles to implementing it.
To do the production before it is economically competitive is just wasteful and potentially more harmful to the environment.
The only reason solar makes any sense over coal is global warming, and to a lesser extent pollution. If global warming isn't a clear and present danger, then solar and most other renewables aren't worth it. We have plenty of coal to run our grid for literally centuries.
If it is a clear and present danger, then it does make clear economic sense to start now well before it's economical. Because the macro economics are that the costs of continued coal use will dwarf any production costs and interest over time. How much is moving NYC going to cost? Miami?
let the market produce whatever is cheaper (using true costs) of all energy production methods
Ok, now what about the century head start oil and gas have over solar? That's not a fair playing field, they have the advantage already just by standing still.
even if you throw out the environment, how about we subsidize US industry to build faster and then sell the results of that R&D through manufacturing to the rest of the world? Because that's exactly what China is doing right now. Or do you want to cede the entire market to the Chinese? The rest of the world WANTS solar in a big way, and yet you're arguing we shouldn't be subsidizing our home grown manufacturing to build what the world wants? Economic suicide.