Kind of hard to help since you don't specify what you've got now. The bottom bracket is crank specific, so let us know what crank (make and model) you have now (and the width of your bottom bracket shell if you know it). The rear hub is probably cheapest to replace with a complete wheel, take a look at our sponsor BicycleWheelWarehouse.com, but it would still help to know specifics of the wheel you have now...
You might also define "worn out", you sure they can't be serviced?
You might also define "worn out", you sure they can't be serviced?