That's interesting because we got a few quotes around 30K euro and so decided against a GSHP. Then one guy who was here about something else came up with a price of 13K euro. He took a very different approach to everyone else. The others took the size of the house and worked out the heating requirement from that, and sized the system accordingly. The cheaper guy looked at how much oil we had been burning to heat the place and sized the system that way. The result was cheaper for 2 reasons. First, the house must be better insulated than the calculation guys assumed; sizing based on actual rather than theoretical load meant we got the benefit of that insulation. Second, because the system was smaller than the others thought it was possible to use the largest unit available off the shelf rather than a special order. I don't know how this might relate to your situation but if you have old heating bills it could be worth calculating things that way.
The 60x40ft area seems quite small to me. How much pipework are they planning to use? We used 800 metres, which was apparently double what we needed. This was in case the smaller GSHP did not cope, so we could add a second one without digging again.
As regards planting fruit trees I would be wonder about 2 things. First, would the roots push the pipes aroundeventually causing leaks? I don't know, but I would want a second opinion. Then there is the fact that trees will take moisture out of the ground and the system works better in wet ground, so how much will this effect the efficiency of your GSHP? Depends how wet the ground is to start with I guess. Again, I would want a second opinion.
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