[andruby]

Sorry, that's not how it works. The network adapts the difficulty to target 1 new block every 10 minutes.

More mining → higher difficulty → higher electricity usage per block.

The transaction costs paid are independent of difficulty or number of miners. Transaction cost depends on the demand. A block has a limited size in bytes. If more people want to send transactions than there is room in the current block, the miner that mines that block will include the transactions that include the highest fee.

When sending a transaction, you can choose that fee. Higher fee → higher chance of being included. Bitcoin clients will usually calculate a reasonable fee for you, based on the demand.