Deal better with region-boundary prices

[Goosius1]

• When a province is near the border with 1. a spare and cheap region, and 2. an expensive and dense region, sometimes the prices can be way to expensive
• This is because the province thinks it belongs to the expensive region, but during claiming, has expanded into the sparse region, thus ending up with a lot more land than it would usually have
• We cannot stop the province expanding, that is way too tricky. Someone has to expand into the empty space, and this is very hard to design or control
• However after it does expand, we can make a more accurate price e.g.
  • The province chunks in the expensive region, should contribute high prices
  • The province chunks in the cheap region, should contribute low prices