adjusting price formula to what's really transactionned

[Cyberpangolin]

After checking, player seems to sell much more items to the store than they buy them. The rate is around 4.5 for 1.

Furthermore, they get tons of coins if they mine, so it's quite easy to be rich enough to buy anything..

So, what I want to do, is to change the formula to have a 10x difference between sell and buy prices instead of the 40% we have now, and get prices really higher for rare items the player wants to buy. This increase on prices would not change anything for commons (more than 5k) items.
Typical prices to buy something:
item ][ price
1 ][ 10k
1000 ][ 100
5000 and more ][ 1

I'm posting it here so you can read it and give your advice. Without any negative remark on august 10th, I'll work on it and commit it when ready.

[BetterToAutomateTheWorld]

Good idea, let's recode this.