Depends on the condition of your motor before you lent it out.
If you have anything done with the bottom end, or the head, (performance wise) pull the head and replace it with another one from here. I've seen lowport heads go CHEAP around here. Just swap your stuff over to the new head, replace headgasket, and go.
If it's just stock, nothing done to it, replace the whole motor. Cheap enough. Just keep in mind what motor you plan on replacing it with, as you may encounter more issues than you think (for instance, if you replace the motor with a highport motor, you'll need to do more than just swap in and go.)