No, fossil fuels really are cheaper than competing energy sources. No corruption needed!
You think they are cheaper when the actual physical consequences of CO2 emissions are priced in? No-one else does, including the fossil fuel companies. They haven't invested the vast sums they have into lobbying and science-interference out of charitable inclinations towards lobbyists, amateurish scientists and think-tank careerists.
Fossil fuels are only 'cheaper' because governments have become irredeemably corrupted by fossil fuel interests, so none have to face public liabilities for the damage caused by their products. The apparent 'cheapness' is a consequence only of fraudulent accounting. This is a specific case of the more general 'Pollution Paradox', viz. "The more polluting a company is, the more money it must spend on politics to ensure it is not regulated out of existence" (George Monbiot).