I built a pool water temp sensor using an ESP32 and a DS18B20. I drilled a hole in the pump intake pipe, installed it and now I always know the temp of the pool.

I cant find the original page I used to build it but it wasnt hard and there are similar guides online. Here is the code I am using on the ESP32

esphome: name: esp-pool-temp

esp8266: board: esp01_1m

Enable logging

logger:

Enable Home Assistant API

api:

ota: password: "fa053faa36e5d6600a5613086aaca3ca"

wifi: ssid: password: fast_connect: true

Enable fallback hotspot (captive portal) in case wifi connection fails

ap:

ssid: "Pool-Espboard Fallback Hotspot"

password: "MCueN8HiEEvS"

captive_portal:

Example configuration entry

dallas:

• pin: GPIO4

Individual sensors

sensor:

• platform: dallas address: 0xE93C01D607349D28 name: "Pool Temperature"
• platform: wifi_signal name: "WiFi Signal" update_interval: 60s

I went with inkbird for something similar. They are Bluetooth, with a cheap wifi module as well. Wide range of sensors. Cost me 60 in total to monitor my hottub temp when I'm in Mexico and it's -40 at home

I know you said "cheap", and this isn't exactly that... but I thought I'd mention it as an option anyway. I went with the Atlas Scientific pool kit when automating my pool. It gives me pH, Temp, and ORP. They also have a dosing pump if you want to automate chemicals. It's based on an Adafruit ESP8266, so you can flash esphome on it, making integration with Home Assistant dead simple. https://atlas-scientific.com/kits/wi-fi-pool-kit/

You can go the DIY route for temperature with a $5 ESP8266 off Amazon and a $1 thermistor, but I don't think there are similarly cheap options for pH and ORP.

If your willing to home brew a solution, check out the esphome project. It’s very easy to implement and runs on very inexpensive esp32 boards.

I’ve got something similar, but less ambitious running at my place (temp only). It’s been solid for about 6 months now.

I don't integrate with home assistant. Not really sure the benefit. I guess asking Alexa to check the temp?

Have you looked into the wifi module? Then it's not wifi only