A rheostat acts like a dimmer switch it restricts the line voltage.
I have never used a store bought rheostat, but I have bought dimmer switches at home depot and wired them inline as a rheostat.
They work well as long as you don’t have too great of a temperature variation in the room the tank is in. This is not a concern in winter, more like spring and fall when the heat is off.
A thermostat is a unit that acts just like your home heat.
You set the temp and it maintains it based on an external sensor probe. It will stay accurate independent of external temperature variations. You would more than likely have to purchase one online if you wanted one.
Thermostats work in two different ways. They act like a light switch and shut off the heater when the desired temp is reached, and then turn back on when there is a sufficient temp drop.
These units are less expensive; I get them for $45 from a supply house and do the final wiring myself.
Usually they range from $50-$100
The other design is a proportional thermostat; it works like an electric dimmer switch, limiting the power to the heater as the desired temp is reached.
These usually start at $100 and go up from there.
If you just have the one tank, then a rheostat will work fine.
Also get a reliable thermometer. The stick-on ones are not too useful.
I use a digital unit with an external probe so you can measure the substrate temperature that the snake is in contact with. You can get one for $10-$20. UTH can get up to 120deg so a snake could get burnt if you don’t restrict them somehow.
TomChambers