100 seems like a lot for just a pillow. However, you use it every night and it helps you waking up without back or neck pain. So, investing 100 dollars into something you use 1/3 of every day seems like it’s basically nothing. My pillow costed almost 200 euros, my matrass was 1800. I’ve had it for 10 years, so it costed me 2000/3650= ~0.548 per night, 7 to 8 hours per day. Almost 55 cents for proper back and neck support, so I don’t wake up stiff and sour. The longer I use it, the cheaper it becomes, but I think in a year or two I’ll buy a new set so I’ll be sleeping like a princess for another 10 to 12 years.
Plot twist: learning to sleep without a pillow is even better for your back and neck. So, there’s your cheap option.