You can not change the gas price of EVM instructions without hacking the core and totally forking off to a new client. This is true for both Geth and Parity.
If the gas limits are not sufficient for you, you can just increase the following configuration options for Parity:
--gas-floor-target GAS Amount of gas per block to target when sealing a new
block (default: 4700000).
--gas-cap GAS A cap on how large we will raise the gas limit per
block due to transaction volume (default: 6283184).
You could try to start with a floor of around 9999999 and a cap of 99999999. And see if this works out for you. Now we covered the limits.
If you want to override gas prices to be accepted by miners, you have to change the following parameter:
--gasprice WEI Minimum amount of Wei per GAS to be paid for a
transaction to be accepted for mining. Overrides
--basic-tx-usd.
You could try to set it as low as 1 Wei.
And to cover your last question: You can not specify gas price in a genesis block.
In private network you can increase block gas limit by using gasLimit parameter in genesis file.
"gasLimit": "0x8000000",
gasLimit in genesis file:
A scalar value equal to the current chain-wide limit of Gas
expenditure per block. High in our case to avoid being limited by this
threshold during tests. Note: this does not indicate that we should
not pay attention to the Gas consumption of our Contracts.
You can read about other genesis params from What does each genesis.json parameter mean?
PS: I have not tried increasing block gas limit but I guess this should work. Although you can increase block gas limit but you should not (ideally). If this is for testing purpose then it's alright. But If your smart contract consumes gas more than block gas limit, this is a concern. You could try splitting contract.
Best Answer
This represents the current Ethereum main chain, and the initial gas limit for that chain was indeed 5000, which was too low to send any transactions. This was part of a deliberate process called "thawing", where the gas limit started out very low, and was gradually increased over time as people became more confident that the network was functioning correctly.
See more about thawing here: https://blog.ethereum.org/2015/07/22/frontier-is-coming-what-to-expect-and-how-to-prepare/
Obviously this value would not be appropriate for a private chain.