But costs a small fortune to run, I would like to know if their ad revenue covers half that cost.
It's definitely profitable. Sports stations benefit from not just "regular" ad revenue but from separately budgeted sports marketing dollars.
Talent is only a fraction of station operating expenses. In fact, the biggest single expense line at most stations is "sales commissions".
Other costs include rent, utilities, connectivity, property taxes, local, state and federal government fees and permits, accounting costs, audit costs, engineering salaries, engineering parts and supplies, office supplies, office staff, production department costs, music licensing fees (even for talk stations for incidental use), vehicle expense, property, manager salary, vehicle and liability insurance, legal fees, collection expense, promotion and advertising, web services, computer equipment and maintenance, cellular phones, travel and entertainment, memberships (NAB, RAB, Chamber of Commerce, etc), maintenance, cleaning and refuse removal, asset depreciation, etc., etc.