Sanduni Upeksha

Hi all, My Nissan d21 has sd 23 engine and it’s little bit hard to start in the morning. All the heater plugs changed recently and my battery is also in good condition. My mechanic says that’s because low compression. I wanna know; - how much is the cost to repair it. - also it has oil leaking issue. So is it better to do a full engine repair? And roughly how much it cost for a full engine repair? thank you