You can do it for free if a) you already have 2 devices, b) don't want to use both of them on the flight and c) dont' worry about the person stealing your bag and simply turning your iDevice off.
BTW, genuine question - which GPS tracker are you thinking of that is less than $40 and will transmit its location to you remotely? I'd be extremely interested in one of those, but I've never seen one for that kind of price.
It may not be as fancy as what this site is offering (not sure since they don't show the product), but you can use an old burner cell phone that has GPS on it to hookup to sites online to track positions of the phone. They also have very long battery lives on them. There is quite a few tutorials online that explain how to to do it for your car, which is the same idea.
old burner cell phone that has GPS on it to hookup to sites online to track positions of the phone.
If by "sites online" you mean "send a text" sure. But that kind of data & gps usage will kill a normal dumbphone battery within a few hours.
These devices use a battery 1/4 to 1/3rd the life of a smartphone's and they use GPS chips or SOCs with integrated GPS that suck power much more quickly that the high-end SOCs you find in iPhones and decent Android devices. They do not have long battery life. Try it. I have.
There is quite a few tutorials online that explain how to to do it for your car
And these tutorials almost always hook the phone up to 12V power. Relying on a dumbphone battery just isn't worth it.
BTW, genuine question - which GPS tracker are you thinking of that is less than $40 and will transmit its location to you remotely? I'd be extremely interested in one of those, but I've never seen one for that kind of price.