Piece of cake, presume the engine is a Z18XE? not worked on a Zaffy before but the engines are the same as the Astra. Remove the camcover, the big plastic cover, undo the bolts holding it onto the cam housing, remove the elec connector and refit in reverse order.
Coil packs are expensive, they are quite rare for the 1.8 for some reason. I know a seller online who sells them for £84 plus postage.
I've just bought a second hand coil pack for the 1.8 as I like to keep spares, I've not tested it yet but if it works ok I'd be willing to sell it on. It's only 1 month old so should be fine but I wouldn't feel comfortable selling something I can't be 100% sure of. If it tests out ok, it will be available in 2 weeks, need to test it that long to be sure, price will be £50 plus postage.