Staying 2 days in transit on way to Australia from uk but 4days on way back

Hi we are traveling to Australia and wanted to see China. so we are stopping in Guangzhou for 2 nights and 4 nights on the return journey. what visas do we require? we are British by birth and hold British passport. the website I went on said it was 151 pound which I think is a lot for the sake of going over by 1 night on the way back 300 for 2 of us. is this correct they said it's the new 2 year one but won't be able to go again so soon? where is the best place to apply? the site was chinese consulate that sent me to CVASC. I know there are so many scam websites thank you