The initial purchase cost of a ground source heat pump system is more than a conventional oil or gas fired boiler. The initial capital expense is offset by lower running costs, lower maintenance and low servicing requirement. There is also the security of knowledge that the majority of your heating and cooling energy comes from the ground and will not increase in price.
Be careful to avoid judging an installation on price alone. It is very important to ensure you have a well designed system if your aim is to save money over the life of the installation.