This is no longer a cheap upgrade, second parts have gone through the roof. Second hand fiesta engines start at approx four hundred pounds,most will need a rebuild, pistons alone cost £500 -£1,000.00 . A recent rebuilt engine sold for £1,800.00 , a turbo will cost £500.00 engine management is expensive to. Sorry to sound defeatist but this now the norm. A cheaper upgrade may be fit a two litre Zetec from a mondeo am sure you can buy a new crated engine for £1,000.00 ish and will give you 150 bhp if mated to good exhaust and induction kit and no need to run a turbo.