I'm undecided on both my best and worst buys - my clutch cost me damn near 2k, so it wasn't cheap, but it's got the lightest pedal this side of a barina, is easier to use than same, and will hold 3rd gear clutch dumps no worries at all

Other good buy would be my lokka - I paid $500 (I think) for a EA diff with 28 spline axles, lokka center and cortina 3.7 gears. IIRC I sold the gears for $150, the housing for $50 and the axles for another $50. So I paid $250 for a lokka and I haven't managed to bust it yet = epic win.
Two worst buys:
Clutch from direct clutches, $630 I think and lasted 5 days, they wouldn't even give me half a refund because they said I slipped it. Epic FUCKTARDS.
Other one was my (up until recently) drive car - an EB XR6.
Found it on ebay, looked great in the pics, offered the woman $2500 after many emails asking her specifically about the condition of the paint, body, mechanicals etc.
Flew to Sydney and got a train for an hour down to her hovel, car was absolutely fuct. Paint peeling everywhere, panels all different shades of red, handbrake inop, hazards inop, radio wouldn't turn off, LHF shock so badly buggered that the wheel could actually be seen bouncing when driving over cats-eyes, etc, etc, etc, etc. Massive list wrong with it.
Bought it anyway so I didn't have to spend another $360 on airfares home, spent probably another $1500 in parts alone (inc the auto shitting itself, and splitting first a heater hose then a bottom rad hose within days of each other) over the next 18 months just keeping it on the road, sold it for 1k recently with 6 months rego. I've got the bitches name burnt into my memory so badly I'll never forget.