S2000 engine will be cheap for the power but is in the region of 3-4k for a package installed if keeping mods to a minimum and engine standard, my engine and 6 speed was £1800 which was a bargain for what it is. tb'd and dry sumped with management your looking at 5k for a complete 255/260hp race engine so they are mentally cheap compared to anything about, and IF it did ever break its a £1500 max job to put a short engine back in it.

Twin piece prop required as well rather than single piece item, gearbox tunnel needs modifying from anything off the shelf and really needs to be dry sumped as oil pump sits where the crossmember does.

IMO I'd go with the Vauxhall, £200 engine, used bodies, AST1612 cams and your banging on the door of 200hp with good torque and when (if) it ever does go wrong its a £200 engine to replace.

I don't personally think a Duratec can touch that sort of power for that money