Low compression on a motor

Hi! I have a 2005 rx8. So I recently went on vacation for a week and gave a remote start to my sister so that she could warm it up once a day. When I come back, the car doesn't start. Put in new battery, new sparks, still nothing. Mechanic did compression test and says that there is low compression on a motor. What's the best way to go around it? Rebuld the engine or just scrap this one and get another one. But I really want to keep this one. Ive grown very attached to it and I cannot just scrap it. Please tell me what options do I have. Mechanic says that he will need to get into this moyor to see whats wrong with it but I think it will be easier to just get a new motor than trying to fix this one.