just depends on the spec you could get the cost down as low as £300 if you wanted to stick with a standard zetec bottom end with a plate to lower the compression all you would need is

1.8 zetec bottom end £150
water pump conversion plate £30
plate to lower compression £30
cheap simple way to block off oil ways £10
arp head bolts £40
felpro comp head gasket £40
some one to make a hole in the sump and mount the breather pipe £10