I think any good 1 - 1.5 gallon gas can would be just fine as long as it seals properly. Why spend 30 bucks when 5 will do?
I carry a plan old square shaped 6 gallon gas can bungee corded to my ATV racks when we took the family 3 ATV trip up to northern WI a few years ago. No problems and really needed it since my 2 older ATVs only hold 3.2 gallons getting 20-25 mpg at best. Only thing I would do at every rest stop is to open the top spout up and let the compressed air out to breathe since a full 5.5 gallons in a 6 gallon container bulges out a little while being sealed up sloshing around all the time especially on an ATV.
I only have room for 1 gallon in my saddlebag, need the rest of the room to haul stuff, I have no intentions of strapping a 5-6 gallon gas can on my bike for obvious reasons. The problem with the 5$ cans, is that they could very well leak in the saddlebag, or like you say, I'd be constantly releasing the pressure, and as forgetfull as I am, that would not work, There would be a big kaaaaaaaaaaaaaaaaaaaaaaaboooooooom and Valkyrie parts and human parts all over the place. Although, iI'd be just tempted to try the $5 can just to test it. Than, how do you know the $30 can would be any different, even??? Just trying to get some opinions, ideas, feedback here.