Cheap = free futon on Craigslist. Just take the mattress.
For a new, cheap, actual bed - Amazon
Foam you will just sink through to the wood. Futon mattresses are better but they are a bit tough. For a proper nights sleep get a coil mattress.
Inflatables are great for 1 or 2 nights. Very comfortable. Get the ones that are twice as high for maximum comfort.
Thank you. You are kind! I will be happy to share with you some of the philosophers I have enjoyed. What I have enjoyed even more is listening to smart people critique these philosophers. They have a way of breaking down the difficult concepts in understandable ways. Go on YouTube and listen to a guy named Rick Roderick. He has 3 lecture series which introduce you to many of the most famous philosophers. I especially enjoy his critique of Nietzsche, Freud, Kierkegaard, Sartre, Habermas, and Hegel. There is a podcast called the Partially Examined Life which is full of really, really great philosophical discussions. One of my favorites is their critique of the movie "No Country For Old Men".
The bed I bought is off of Amazon, strangely, and it is awesome! I cannot recommend it will be as comfortable to you as it is to me. I am a very large framed dude and this one worked wonders for me.
It is available in many sizes, and very, very affordable. Again, I cannot promise you a good night sleep on it, but it is perfect for me.
Finally, for the science fiction reading I would suggest starting with the best SciFi book ever in my opinion: Ready Player One by Ernest Cline. It is just too good to put into words.
Enjoy your time on this Earth. Relax, friend. You will find your place. I promise.
In lieu of buying a second hand mattress (ew.), if you have Amazon Prime this is a pretty darn good mattress for the price. We have a king, and I have honestly had the best sleep of my life on it.
How cheap? You can buy a mattress on Amazon for $189. They're pretty great and comfortable! Plus, they're super fun to open because they come in a tube and then expand magically.
I bought this on Amazon recently. The matress comes in a vacuum-sealed bag and decompreses as soon as you open it. They have versions with either springs or memory foam. I got a full, but as you can see they have other sizes.
Keep in mind that you can buy a pretty good twin mattress on Amazon for $150 with free shipping.
It looks like there's also one for $83, also with free shipping.
Get the signature sleep contour mattress off Amazon ($150 for a twin), it's cheap AF and surprisingly comfortable. :) Here's a link