Hi try using the following:
geth --dev --mine --minerthreads 1
--dev Developer mode: pre-configured private network with several debugging flags
--mine Enable mining
--minerthreads value Number of CPU threads to use for mining (default: 12)
This runs a private testnetwork with your own chain. The miner runs low on one thread to generate new blocks and this way you get testnet Ether in your private network which can be used to pay the fees.