Do you like the idea of a streaming media stick for your TV, but find that even Google's Chromecast or Amazon's Fire TV Stick costs more than you're willing to pay? You'll want to visit your local Walmart, then. The big-box retailer tells GigaOM that its Vudu Spark dongle, teased at the FCC back in November, is already available at 2,400 stores for $25 -- that's at least $10 less than its big rivals, and as much as the upcoming Matchstick. More stores are coming soon, Walmart adds. It's a tempting offering, but there's a good reason why it's so affordable. As hinted earlier, the Spark is only useful for watching Vudu purchases and rentals. That's fine if you're not picky about how you get your movies and TV shows, but you may have to shell out more if you're determined to use Hulu, Netflix or any other online video service.