The K20 swap is possible, if you pick up the latest issue of Honda Tuning they have a tech article about swapping a K20 into a DA Integra, so you might want to check that out. I'd say go for the K20 if you can get it for that cheap. It's got tons of potential as far as tuning and modding possibilities.
I hope you realize though that the tranny that's in your car is not going to bolt up to either of those motors, so I hope your prices are including transmission as well as just the motor.