A good air source heat pump (I ordered a Mitsubishi Zubadan 11,2kwh in November) realistically costs around 15k installion included. Some brands are even more expensive (NIBE), others a bit cheaper (Daikin, I would avoid them).
Ground source isn't worth the extra bother. You'll easily pay more than 8000 for drilling the holes alone. And if you have a cold winter, your heatsource might have cooled. Your coefficient of performance is also, at best, one point better.
Don't buy if you don't have floor heating.
At worst we'll be better off 1200 a year. At best 2100. Lifetime estimate of the system is 20 years. You get a (very japanese) 5 year garantuee... Long live the green madness