The worst survival ordeal that I've had to endure was eating fried liver at a dinner where I didn't want to appear rude, by gagging and retching. So I don't speak from much "experience" in such things.

But with $30 to prep for survival, I'd want a knife, fire making, and water purification first. Right even with that I'd want some way of signaling. Obviously I'm thinking more of outdoorsy survival than urban survival.

For $30, I should be able to get a Mora, a Bic lighter, some iodine tablets (or even cheaper a bottle of liquid iodine), and a whistle. I might even be able to substitute one of those mini purifiers - a Sawyer straw perhaps - for the iodine and still slide in under $30. I know this thread was more about "inexpensive survival items" than "everything you can get for under $30 total", but still, I would lean towards the Mora, Sawyer filter, Bic lighter, etc. as highly recommended items for under $30 (each).