May I ask, how you expect the circuit in post #1, to deal with these factors?
Will voltage rise above 35V? How high will the voltage rise to? What is the maximum voltage you expect at the input? If you do expect voltage greater than 35V, then you will need to use other regulators.
Why negative voltages? A single diode at the input will protect against negative voltage (as shown in circuit posted in #1).
If you do want to go the switching regulator route, you can take a look at LM2575. According to Newark, it's cheaper than AP1512.