Honestly,
I'd definatly start from a cheap base vehicle that has good potential and spend the "spare" money on uprating/upgrading as you need it to be.
Because even a new car will need to be modified for what you're looking for and that means you're spending even more money than the new price + that the mods most likely invalidate your warranty anyhow.
As for the scenario of cooking oil mixed with the diesel.
On a petrol car, like the Prado, you could LPG convert it and maybe ensure, that you have an option to refuel from gas bottles, if LPG isn't available. Gives you a second/cheaper option for fuel. With a dual pickup on the LPG tank you could even also feed gas applieances like a cooker then.
/M
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