I can't recommend any cheap places to say, but depending on how old you are, you could always try a hostel of some sort.
I went there with my dad in the spring of last year and fell in love with it. It's a beautiful city with lots of great energy. I will say that you'll probably find yourself photographing the Brandenburg Gate quite a bit, as I found myself doing. That area is quite touristy, but with good reason. The Tiergarten is a beautiful park that's great for a casual stroll. Also, check out the former east side of the city. It's quite different than the more famous west side, and seems to have gone through a real renaissance in recent years. The Friedrichshain/Kreuzberg area is quite hip, with lots of artists and musicians hanging about doing their thing. There's also the East Side Gallery, which is the largest continuous stretch of the Berlin Wall in the city. Certain sections have been white washed and given over to artists to paint on, and there are other sections that are still as they were when the wall came down. Haunting, overall, but pretty cool.
Overall, the city is very walkable, and extremely easy to get around via the trains. I would love to live their some day.
Here's my Flickr set from my trip, all on Kodachrome, Ektar 100, Provia 400X, and Tri-X with an Olympus OM-4.
http://www.flickr.com/photos/maclaine/sets/72157622022394375/with/3858748410/
And some of my favorites.