I bought one of these:
https://www.amazon.com/dp/B0B63FV7FR?th=1
with these batteries:
https://www.amazon.com/dp/B0BN1ZVS5X
Total is about $75.
FYI the range is only a few miles so a lot of people buy two devices to try it out if there are no other devices in your area to connect to the mesh. You can look at a map of people who have devices with location enabled and connected to MQTT here: https://meshtastic.liamcottle.net/
There are more nodes in the wild than are shown on this map, but it could give you a good estimate of whether you can expect to connect to the network with only one device.