So with that post about a cheap air filter that hit the top, where is the best place to buy a cheap merv 13 (wildfire smoke) 20x20x4 air filter?

Bonus points for canada but if I have to buy from america I can see if they ship to canada.

People were saying any higher merv rating is too restrictive and this was a happy medium. Also that the 1'' thick filters weren't good compared to the 4'' thick ones.

This is the cheapest I've found so far.