Taken from Google.
Multiplex Costs

Multiplex capacity fees vary from multiplex to multiplex. However, as a rule of thumb, the cost of carriage for a mono (64 kbit/s regular DAB) service on a non-London multiplex is around £3,500 to £6,000 per month.

For 32kbit/s in DAB+ the fees, can range from around £2,000 to £5,000 per month.

To broadcast on a London multiplex generally costs double.

For a national multiplex capacity would likely cost in excess of £30,000 per month.

In addition, there may be some additional costs of connecting a service from your studios to the multiplex centre. This cost would vary according to your location and the relevant multiplex centre but could cost around £500 per month.

Ofcom Costs
There is a one off application fee of £250 to apply for a DSP licence, and an annual licence fee of £100.