Two weeks after finishing my undergraduate education, I began medical school. After including books, various exams that would typically cost $1,000-$3,000 per test, and medical school tuition, my yearly education costs amounted to $45,000 per year.
Radio network time can be bought more efficiently, so let's say $1MM on radio, $300k on print, $250,000 on cheap inventory online banner ads, $500,000 on paid search engine marketing (assumes you have a website to point to). Again, all of this is per month.
To illustrate this, the cost of advertising on one billboard for a month is anything from Â£500 to Â£1,500 per month. Costs do fall substantially on a per billboard basis for larger campaigns but the overall cost means that only larger brands can afford this form of advertising.