I see this erroneous thinking time and time again.
A brand new (non-refurb, unopened, unlocked) iPhone SE has never been sold anywhere for under $200. It has never happened. The $99-150 iPhone SE's that you've seen online are either pre-paid phones (contract-based) or refurbished. If you buy any of the super cheap brand new iPhone SE's from the pre-paid retailers, you will not be able to use it with other carriers, until the contract is honored. Most of the time, this means having made several months payment on the plan that you agreed to before the phone can be unlocked. In some cases, it will never be unlocked.
Let me repeat: a brand new unlocked factory-sealed iPhone SE has never been offered for sale under $200 anywhere online in the 3 year history of the device.
I'm not sure why people always think that this was and is a $100-200 phone. It's not. Never was. If you want it unlocked, brand new, and factory-sealed, you always had to pay $200+ for it.