For quite some time now, we have endured a barrage of "only $19 a month" contributions to this and that advertisements. So why the magic number $19 and how many of these are there.

Same reason everything is $8.99 instead of $9.00 or $29.99 instead of $30 I reckon. It gives the illusion of being much less expensive.

I don’t know how many times I’ve heard someone refer to a $9.95 item as costing “nine dollars.”
Those people will look at the 1 in the $19 and think $10, not $20.

"....For only 63 cents per day....."

Gasoline is another item which traditionally always had an extra .9 cents at the end.

forget them. I donate, but if you ask me to go on the hook for you, FORGET IT. I am done.

I seem to recall there being various marketing studies that set $20 as one of the price points where people start putting more thought into their purchases. That is, the average person is more likely to impulsively pay for something that costs less than $20 than something costing $20 or more.

Other studies show that people also tend to put more emphasis on the leftmost digit(s) in pricing, and therefore subconsciously associate prices ending in 9 with the lower whole number represented by the left digits, and not rounding up to the actual closer whole number. Hence, someone seeing $19.99 might subconsciously peg it as $19.00, and therefore cheaper than the same product priced at $20.

Those together are why $19.99 is such a popular price for products.

I could see $19 used for similar reasons. It's under $20 so folks are less likely to put a lot of thought into it. And some will subconsciously associate the $19 with $10.

The son had Planet Fitness, at $10 a month. He moved and that was almost the end of it, that’s what they want.

I saw the charge & investigated. It took ‘registered mail’ to an address to cancel. I jumped through the hoops to cancel. There is are lot like that, a reason one has to take a peak at the CC statement.