Healthcare in this country is so expensive because of Medicare and Medicaid. Because the healthcare industry is subsidized, there is no reason for provider to control their costs. For decades now, costs have been passed on to the taxpayer through these programs, but now it's not possible to wring any more money out of taxpayers. Without these programs doctors would have to price their services so people could afford them, otherwise good luck making enough money to live. Another reason costs are so high is because the number of doctors is kept artificially low by organizations like the AMA so that doctors can charge more for their services.
In 1900 there were about 500,000 licensed doctors in the US which had a population of 100 million. Today we have about 600,000 doctors with a population of 300 million. But the numbers are worse than that. There are far more specialties today than there were in 1900 and fewer doctors are going into general practice so the reality is much worse than the numbers would make you believe.
Despite what Esoteric says allowing insurance companies to sell across state lines would drop the cost of insurance dramatically. Because states have enacted protectionist laws favoring in-state providers, those providers can charge whatever they wish and you just have to pay it. Opening those companies up to competition would force them to lower their prices, lest some other company move in and steal their customers through lower pricing. Price is, after all, king when it comes to who people choose to go with.
The only problem is that then politicians could not count on campaign donations from their favored insurance companies, so don't expect changes any time soon.