Dumb phone required for Bluetooth data tether?

I have an Apple iPhone 5s and a Nokia 1201 with two different phone numbers from different carriers.

I have unlimited data and minutes on the connection for Nokia 1201 but cannot use the sim on the iPhone. Using this sim on the iPhone 5s is off the table for my own reasons.

Here's the problem:

I want a dumb phone for $100 (unlocked) new/used which can take the sim and then tether the data with my iPhone using bluetooth. Anyone using a similar setup with their iPads/tablets? Any other suggestions?