If you have the right credit card, you can essentially get TSA PreCheck or Global Entry for free. It typically costs $85 to apply for TSA PreCheck and $120 for Global Entry. Dozens of travel credit cards come with a benefit that reimburses that cost when you use the card to pay the fee. The reimbursement usually appears as a credit on your statement.
Keep in mind that these cards don't guarantee that you'll be approved for TSA PreCheck or Global Entry. You still have to go through the program's background and security checks, and you could be rejected. But the statement credit means it ultimately won't cost you anything to apply.