Well, cams are a doddle to fit. It takes about 10 minutes to get the belts off and mark up. About 5 minutes to remove the rocker cover. Then about 5 minutes to crack off the cam bearing caps.
The only trick is getting the timing right on a new cam.
Whereas a bottom end is a bit more hard work. You'd need to drain the oil and coolant, remove the belts, alternator, PAS pump, water pump, water hoses, starter motor, gearbox, then crack the head off, replace the head gasket and bolts, new oil and filter with new block and a fresh batch of coolant.
The coolant, oil filter, oil, head set would set you back about £40-50. You'd need the TSR spacer for the dizzy though, not sure on price. The blocks can be picked up cheeeeep, usually <£100. The work itself isn't hard - as long as you have the tools. The knowledge you gain from doing it is invaluable though!
I'd throw the £400 at a decent socket set, £100, a decent torque wrench, £40, a new clutch, £60 and the block and bits from the above. You'd come in under budget with more power and a decent sense of satisfaction
