A heat pump will likely be more expensive than just a furnace or boiler. But after state rebates and federal tax credits, the cost difference may be less dramatic. And when you combine that with the fact that a heat pump will meet your entire cooling need (meaning you won't need to replace your air conditioner in the future), you may spend less in upfront cost for one heat pump system, versus a furnace / boiler system plus an air conditioning system.
Moreover, if your home is heated with high-cost fuels like oil or propane, your heat pump can save you on heating by meeting most or all of your home's heating needs.
Lastly, new HVAC systems (especially heat pumps) improve home value. According to
one study, residences with an air-source heat pump see a 4-7% price premium versus other homes.