Normally the costs are borne by the producer. A broadcaster will be involved--to a relatively small portion of the budget, to 20% or 30% perhaps—but the costs are incurred and financed by the producer.
Sometimes broadcasters will get involved in an equity manner, where they take a share of the production. But generally they acquire a licence to exploit the show in a certain way, for a certain period of time, and for a certain fee, which is usually 20% to 30% of the budget--roughly, in a very general way.