I think that covers all the basic trims so now engines......

1.4 and 1.6 zetec-se engine.
Total pointless in a ford focus as there to gutless and cost just as much as the 1.8 zetec-r engine and it should have stayed in the fiesta (well yes before anyone says the focus was the first to have 1.6 but it shouldnt have been fitted in a car so heavy)

1.8 and 2.0 zetec-r engine.
Both good runners which are very simmar in power and mpg ect but the 1.8 is the cheaper to run and buy and unlike the 1.4/1.6 the engines its not weak as hell and if your looking to keep it as cheap as posible i would go for the 1.8 zetec-r as it has the best of all worlds.

1.8 tdci and tddi
I really cant say much about these engines in the focus but these would only be suited to high motorway milage.