Tie rod ends are a ball-in-socket joint. Once they wear out and become loose, they must be replaced before they pull apart. The estimate you received is very reasonable for this job. I would have expected the cost to be higher. As to waiting around to get this fixed, I wouldn’t wait too long. Your tie rod ends connect your front wheels to the steering system, allowing you to point the car in the direction you want it to go. If one breaks, that wheel will turn in whatever direction it wants to. The best that could happen in that situation is that your car will be disabled and will have incidental damages to the front suspension, brake system, wheel and tire, and possibly the fender. The worst that could happen is that you will be unable to bring the car to a safe stop on the side of the road, will crash and/or roll the car, and people will get hurt or killed and property damage will be done. Criminal charges could also be filed if this happened and the police found out you knew repairs needed to be done to the steering system and that work was neglected. Tie rod ends are part of the second most important system on your car, steering (brakes are number one; what good is a car that starts if it won’t stop?), and in the interest of safety should not be postponed or forgotten about.