I dont know for sure off the top of my head but isnt a Toyota Hilux going to cost way more in fuel, tax, insurance, tyres etc to run than any of the other two? The cost of a car isn't only what price you pay for it, you have to consider running costs... and common sense would tell me a huge 4x4 will cost significantly more to operate.
EDIT: After a quick look, the Hilux gets about 20mpg (ave.) less than both the Auris and the Yaris and also has around double the CO2 emissions. This will make road tax about 4 times more expensive per year and god knows how much more expensive on fuel (also taking into acount you are mostly an urban driver). You're clearly not taking this into consideration. A couple of grand of a difference between the Hilux and Auris will seem insignificant compared to the difference in running costs.