Monster's Adidas-branded Sport Adistar In-Ear Wireless ($100) is one of the better fitting in-ear wireless sports headphones -- and it also sounds decent for the money. Another good choice for dads who run.
Amazingly, Amazon's Kindle Paperwhite e-reader is actually more expensive than the Fire tablet. But this $119 unit is often discounted to $99. It's a good choice if Dad is a bookworm who enjoys distraction-free reading.
Turning to video streaming: There are plenty of Roku models at $50 or less. But in the $100 range you'll find the Roku Premiere+. It's worth the extra cash if Dad has a 4K TV with high dynamic range (HDR) video compatibility. But even if he doesn't, he'll like the Wi-Fi remote (no pointing needed) with a headphone jack for private listening.
If you want to nudge Dad to a healthier lifestyle, a fitness tracker is just the ticket. The Fitbit Charge 2 and Alta 2 will cost you around $150, but you can snag the more minimalist Flex 2 for closer to $90.
Another good gift for outdoorsy dads: Biolite's $80SolarPanel 5+ is equipped with an internal battery that stores energy from the sun, which means he can keep a charge in reserve your for phone and other devices, although tablets will take longer to charge.
Another good gift for road warrior dads: The Mophie PowerStation Plus, an external battery charger starting at $60, has an integrated Lightning cable with a micro USB adapter so he can charge a variety of devices.
The NES Classic would've been the perfect retro gaming gift for Dad -- except for the fact that Nintendo just discontinued it. But don't pay big bucks on eBay -- get him a Nintendo 2DS instead. At just $80, it's the most affordable way for him to relive his childhood with games from the Zelda, Metroid and Mario series that he can't get on his phone. Even better: Mario Kart is thrown in for free.
If $100 is outside your budget, don't worry: We have a whole separate list of great Father's Day gift ideas for under $50, too. Spoiler alert: The Amazon Echo Dot shown here is at the head of the pack.