Q: someone added oil to brake fluid and hyundai sez entire system needs replaced at cost of $4000; are there any alternatives?

Motor oil damages ONLY the rubber components in the hydraulic brake system. Those rubber components are limited in extent and thus all of the rubber components at issue would fit in the palm of your hand. The problem is the rubber components (mostly seals but some rubber hoses) are scattered throughout the brake system and are buried within more complex parts such as the calipers, the master cylinder and the ABS/Traction control system pump which you probably have. If the brake function is already altered, that likely means that the motor oil has caused these seals to swell. If the oil contamination is extensive enough, eventually the brakes could become inoperable, the timing being uncertain. Four thousand dollars seems on the high side to rectify this, even if all parts are just replaced outright. You probably would save money getting a quote from YourMechanic and if you desire to do that, just request a comprehensive brake system inspection and the responding certified mechanic will evaluate what the situation is and provide you a complete written estimate at that time. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.