Are you offering websites with affordable prices, or offering websites at affordable prices? "With" means that the websites come with affordable prices. "At" means you are offering the website for an affordable price.
In simpler terms, if you are making websites and selling them for cheap, it should be "At".
Im basically saying that im selling affordable web hosting which can bring customers websites to life (customers buy affordable hosting and work on site, bring it to life, make it grow, etc.)