I hate to be the bearer of bad news, but $30 is definitely on the low side for getting a good DVD player.
If you look at Walmart, Best Buy, and Amazon (websites anyway), Best Buy has no non-refurbished DVD players under $30. Walmart has 2 under $30, and neither really looks like a decent one. As for Amazon, I don't think they even have any under $30.
My best advice is to hope a local Walmart store has one of the Magnavox DVD players that come in a red and white box that's maybe 3-4 inches tall, by about a foot long and maybe 8-10" wide (note: I'm terrible with sizes when I've got to guess). I picked one up a couple years ago for my mom to use and it's worked like a champ.