Your pet store is pricey. I would try Amazon. I can't attest as to whether this brand is specifically ideal for Triops, it'll probably work fine, but just using it as an example, it's $4.08 for 184g and you don't have to worry about the risks of buying from bulk eBay sellers.
I just used these for the food because I don't expect beginners to be feeding live foods or using expensive food tailored for every species in their tank.
But yes you're right! It's just for the one tank. Most people get multiple tank syndrome eventually but I figured it'd be unfair to start out with three 100 gallon tanks and only one dog lmao. Besides look at how much you can save every month by not getting one dog and you can save up enough to get your next tank in no time :)