TarHeelAnts has a variety of different formicaria up for sale on their website which are very aesthetic and can simulate the natural environments that the ants live in.
Ant Keeping Depot has products from different vendors and makes browsing through and comparing different products easier on the users. They sell formicaria, tools, feeders, and all sorts of appliances for ant-keeping.
LCM lab is one of the cheapest vendors for glass test tubes. They sell tubes in bulk. Test tubes are one of the most useful and reusable founding nests for keeping ants.
Many ant-keeping vendors sell their products on amazon and ebay. Test tubes can be found there as well.
Dollar stores like Daiso and Dollar Tree often have great deals for plastic containers!
There's a good chance some tools or ant foods can even be found at your local hardware store!
Pet shops often sell heating utilities, food and tanks which could potentially be useful for ant-keeping!
The discord server is split up into regionals, which makes it easier for ant-keepers from the same area to be able to reach each other. The community is also a great way to verify the legitimacy of the ant vendors and look for the most trusted or cheapest option.
Buying and selling is permitted on formiculture as long as the users follow the forum rules and post their general location on their profile. Many users have sales pages for their ants, and the private messaging service allows vendors and buyers to contact each other.
AntsCanada's GAN project might be a good option to buy ants in areas that have less ant-keeping activity. However, there is less of a guarantee on the ants and the general pricing.
TarHeelAnts sells Pogonomyrmex occidentalis, which can be shipped to most states, excluding California, Florida and Hawaii.