Reco's for the above please, fully compatible also with either TMO bands, or MEID whitelisted in ATT

How old / cheap a Pixel would work?

Not talking as a SIM activation phone approved by their IMEI checker, already have a 4G Moto Pure works for that

just one that de facto works with an already activated SIM

Prefer under $200

used off Swappa or eBay if necessary