If you need a very basic oscilloscope for DIY use then definitely take a look at the DPScope SE. It sells for under $60USD as an unassembled kit that includes everything you'll need minus the probes and the USB cable.
Bandwidth, sampling rates, and resolution are quite limited but for the price you still still get an excellent set of features including triggering and FFT spectrum analyzer functionality and you won't be able to beat the price for a two-channel oscilloscope / logic analyzer. The software is fairly well done too and I find it very easy to use. ADC sensitivity is around 4mV and there is no AC coupling mode, but you can achieve AC coupling by means of a series capacitor. [Specs page]
The DPScope is also very easy to assemble (if you're reading this I assume you have prior soldering experience anyway) as it utilizes only through-hole parts and excellent documentation is provided. I was able to get it up and running in one go. Assembly time took approximately two hours for me and I'm a pretty slow solderer.
Project page: http://www.pdamusician.com/dpscope/overview_se.html