Is buying a 2004 Chrysler Sebring Convertible with 60,000 miles worth 3500.?

If it has the 2.7 liter stay away. Without knowing more about the vehicle hard to say what it's worth, but the price is inline with whats listed online.....

all sebrings are worth 5,000 at least

This model if purchased from an individual should range from $4500-5500 based on condition, and possibly more if equipped with navigation and abs. I would say $3500 is a bargain if you know the seller (and the car was cared for), or you get a mechanics approval. Unless garaged, a 2004 will exhibit sun fade/damage to interior, and the top will be worn. The most important check, in my view, is whether sludge is present in the engine. The 2.7L can be prone if oil is not changed faithfully, or under severe conditions like lots of stop and go. I recommend synthetic oil be used, because it flows better in all temps and suspends contaminants better, preventing sludge formation. Good luck!