Good local-only/local-first wifi thermostat?

I want to be able to control my thermostat from my phone, so I'm looking for recommendations for one that meets the following:

• Works with no network access (as in, I can access it but it can't access anywhere else, enforced via VLAN on my firewall)
• Lets me control my single apartment thermostat (temperature, heat/cool, maybe programming but it's okay if I have to do that on the unit directly)
• Not hundreds of dollars
• No microphone

Any thoughts? Really just want something simple.

Edit: I have no other smart home devices right now, if that matters.