I'm not sure about the Portal Store, but the Interagency Visitor Center charges $2.50 per night. They also have a dropbox where you can return the canister after hours too.
I usually rent Bearikade canisters
online . If you rent the Expedition (longer) you can hold a purported 8 days of food as opposed the 5 the common Garcia cans promise. They are more expensive to rent ($6 per night) but they are lighter, sturdier, more spacious, easier to get stuff in and out. They also ship them to you.
I also think they can cut you a deal if you are renting them for a thru hike like the HST, check out the site and give em a call!
