I'd personally say stick with the B18C1. Is there any particular reason you want to get rid of it? I was always happy with mine.

H22A swaps are more diffucult, they require a custom mount kit, you have to cut off the upper tranny mount, require custom axles and you need a rather pricey shift linkage mounting plate (Preludes use cable shift linkage as opposed to Civic's rod linkage). I don't know if it's cheaper or not but I wouldn't really think so, not by a large margin at least.