There are reports that oil, coal and gas industries in America have invested more than half a billion dollars on lobbying against acting on climate change. In Australia there are more than 540 'registered lobbyists, + many more unregistered. So I'm wondering how many of these are in the oil, coal and gas business, and how much do they spend on their lobbying?
How much have carbon-based industries invested in anti-climate-change lobbying in Australia?
This article tackles some very similar to what your asking and I think it provides an insight into the order of magnitude of Australian anti-climate-change lobbying spending:
The five largest global oil companies – ExxonMobil, Shell, Chevron, BP, and Total – have spent a combined $US1 billion ($1.44 billion) on “misleading climate-related branding and lobbying” in the three years since the Paris Agreement was signed, according to research from InfluenceMap.
The same article provides a small graph to have a visual representation:
While this certainly does not cover your question entirely, $US1 billion is a very rough figure to understand the size of the lobby in oil, coal and gas business related to climate change.