What is the best and cheapest way to insulate garage?

[Racersk]

Home Depot foam velcro'd to the fronts, and foam across the tops. Just put a 300W in my 55 and raised temp from 65 is to 81 in a day no problems.

It's cool to see my oscar play peek a boo with me when I take the foam off...Cause he knows he's getting fed, lol..

 

[Tom LoFaro]

I think the cheapest way would be to insulate the tanks instead of the garage, and I'd go with the thermal blanket idea