you can get a nice pair for about $20 right here. been using them for 2 years and everything still works great. main thing is you want to get a very sturdy cardboard to use for the bottom bc it doesn't have any support. just grab a box from costco or some other store if you can.
I think the XL plus size is the perfect size. fits 2 columns of stacked to-go boxes in bags, the kind you get from asian restaurants etc. also fits the very large bags you get at outback or red robin perfectly. not too big that a regular order will swim it though, usually.
I paid like $11 for two from Amazon.
Edit: price went up but I've had them for seven months for three services and they are still holding up. There are also plenty of options on Amazon.
https://www.amazon.com/gp/aw/d/B071ZNFVMD?psc=1&ref=ppx_pop_mob_b_pd_title