1998 Plymouth Neon Should I replace the engine??

I have a '98 Plymouth neon. The body is flawless and it drives like a charm. Unfortunately recently I have found that there's oil in my car's computer. It stalls nervously. I thought it was the spark plugs but we fixed that, thought it was the battery but I replaced that... So I was curious how much it would be to replace my engine. It doesn't have to be the latest and greatest thing but a new engine. Or am I over my head?