How can I make a cheap sauna?

You need to choose some wood, it's slightly more expensive, but it will work well with the sauna.

Traditional Outdoor Barrel Sauna Kit

Solid Wood Type : Hemlock/Red Cedar
Function : Wet Steam, Wet Steam
Door Glass ：8 mm tempered glass
Heater ：6kw Stove
Voltage : 220V
Specifications
Range in size, from 6'W x 4'D x 6'H to 6'W x 8'D x 6'H
Sized to fit: 2 to 8 people

phone, and has a resonance effect, just like a stereo sound.
Operatting Temperature Range: 0°C - 90°C / 32°F - 195°F
Application : Outdoor