If it has some sentimental value, then go second hand engine. You can find lowish km Z18XEs pretty cheap, as wreckers generally don't sell many of them. If you're handy with the tools and you have access to a crane, it's not a hard job to swap the engine out. Just remember you will need new timing belt and water pump too. If you can do it yourself, or have a mate who'll do it for beer money, you could get it done for around a grand.
As someone who has completed a couple of engine swaps, unless you're buying a whole car with the 2.2 in it as a donor, I wouldn't bother trying to swap it in. It can be done quite easy and it will fit, no issues. You just need the whole car so you get all the parts you need. 2.2 however, won't fit the 1.8s gearbox (you'd need to use the 2.2s box, shafts and hubs). I helped a mate a couple of years ago with his Astravan swap in a Z20LET, it was so much easier swapping in everything from a donor car, that's for sure.