As someone who has swapped from K-series to Duratec, here's my thoughts. It's expensive whatever anyone tells you. Anybody who says they got change out of £10k is either an expert in man-maths (i.e. deluded) or used a stock engine (probably second hand) and managed to get lots of parts second hand or on the cheap. For a brand new 250bhp+ engine it's nearer £15k with all the ancillaries, exhaust, etc. Never underestimate the cost of the "little bits" - the plumbing and wiring soon mount up.In mitigation you can make a fair bit back with the K-series bits, Dry sump is especially valuable. Second hand engines are worth very little in one piece - I sold mine in bits and made more than I would have as a running unit. It still won't be as much as you'd like.Duratec was a "legacy" engine even when I fitted mine 4 years ago but it does have wide support both in terms of spares and 3rd party support so probably not a big issue.Ecoboost definitely worth a look but get a ride/drive in one first as it's a very different beast to a K or Duratec. Cheaper install as the engine is virtually stock but there are additional requirements like an inter-cooler. Buy a bigger turbo = 300bhp/300lbft which might be quite fun :-)You'll need a catalytic converterDepending on how much you paid for the chassis and bits, it could be a bargain route into a high spec car or a ruinous folly.