My research also lead me to one of the newer, more expensive phones. (wanting a physical keyboard limited my search greatly. Also finding out that modern smartphones don't always STAY unlocked, meant I had to stay with t-mobile phones.) This made the ebay game hard, but I got a nice deal on a used one, so being cheap was satisfied. It makes my hands smell like month old cigarette smoke, but I expect that to go away soon.
I got a Samsung Galaxy Relay.
As I said, I was just expecting a lot of work and a bit of aggravation. The phone I've been using for a while now doesn't always deal with my lack of data that gracefully. But here's the great thing. It did exactly what I could hope for. Other than the fact it wants a new sim to enable WIFI calling and a little aggravation with moving my contacts it seems to be completely happy to use wifi or not. Completely happy to send MMSes to email addresses with no complaints. It's been a long time since I've been this happy with a product.
And the contact list thing is a little weird, but would have worked fine if I had just known the trick, so I'll explain. I couldn't import my t-mobile saved contacts with wifi on because t-mobile wants to do it over it's own network. Since I have no data, I assumed I would just have to work around that, so I spend a while getting the contacts from my old phone into a format that I could upload meaningfully to google (since it was having no problem updating contacts from google.) I succeeded, was done fiddling for the evening, turned wifi off and then noticed that now it was more than happy to download my t-mobile contacts. Since it expects contacts from multiple sources it dealt cleanly, but it's interesting that even thought I don't have data on my plan, there are a few services t-mobile will still let my phone use.
I can't believe how well it all worked. Yay!