1989 Honda Prelude My car battery goes dead after sitting o

Recently if my car sits over two days without driving it wont start and I'll need to get a jump. Had car diagnosed at reputable place, their diagnosis: Battery checks marginal recomend recharge, alternator ok, starter ok, FOUND EXCESSIVE DRAW, MEASURED 350MA SHOULD BE BELOWN 100MA. VEHICLE HAS EXCESSIVE DRAW WITHIN ELECTRICAL SYSTEM. Further diagnosis required. Inspection for excessive electrical draw $220.00.

What is this? Is this serious for my car? And expenses? Is this costly?

AWW AND ITS CHRISTMAS TIME! SINGLE PARENT PLEASE HELP ME UNDERSTAND!