Have a drive thru oil changer or shop handle this and you can check repair prices here www.repairpal.com/estimator and find a repair shop here www.repairpal.com/directory
A reputable mechanic can test the radiator fluid to see if you have a cracked engine head or a leaking Head gasget. Probably Oil in your Antifreeze causing it to be black. Sorry but it sounds like you have some major repairs that need to be done ASAP.
RepairPal Certified shops can diagnose and repair your 1994 Lexus ES300. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.