DGPS Signals come in many forms. The *major* types of interest
to casual users are:
1) Signals provided by the US Coast Guard or "the government" in the 285khz to 325khz frequency range. These signals are usually "free". At least in the USA.
2) Signals provided as subcarriers on FM broadcast stations. An example of this is DCI here in the USA. These services cost from US$75 per year for 10 meter corrections upward depending on accuracy of the correction services.
3) Signals provided over wide areas of the earth by Satellite. An example of this is OMNISTAR. The equipment and services on this type of service are expensive but provide corrections "virtually anywhere". The OmniStar receivers typically cost $2500 or more.
Have additions/corrections to this information?