It is not the price it is intrest. Renewables cost a lot of money in the beginning, but are pretty much free afterwards. For example first you have to buy and install the solar panels, but then maintanence is very rarer and basicly free for years. However fossil fuels are cheap in the beginning, but expensive later on. So when you buy a diesel generator, the generator is initally pretty cheap, but you have to buy diesel every time you need power.

The solution is to set up a large fond, able to invest in many poor countries and spread the political risk. Preferablly guranteed by a large rich country outside it. That might end up as one of the best investments possible for everybody involved.