Does anyone have a favorite place to buy cupcake/cake boxes or plastic containers that is cheap?

Dollar tree!  Red plastic bottom half, clear top, a snap on each of 4 sides with a handle on top, indents in base to hold 9... they're more than great for only $1.00 and reusable (rather than Hefty foil containers).

No that is not cheap people are enjoying cupcake, cake boxes or plastic containers and those are reusable.