The surest way to get Pre is to have a Known Traveler Number. You can get that by applying for Pre or Global Entry. Keep in mind that the $85 is for 5 years. Also, if you travel internationally at all you might want to think about Global Entry instead. It is $100 for 5 years, and it includes Pre. Makes a huge difference in clearing immigration when returning to the US.

If you travel to Canada regularly then you can also look into NEXUS. It, as I understand it, is $50 and includes GE and Pre.

Also, please keep in mind that the fees are actually paying for the background check. Paying the fee does not guarantee you acceptance.