I read one blog post about detecting an (already known) exoplanet just using a telephoto lens and a DSLR. So it's definitely affordable!
I've read about amateurs detecting them with their instruments, like 12" SCTs. I don't know when I'll be able to afford it (probably a small Meade, SBIG CCD, etc.), but I'll definitely be writing my own algorithms/code to process the data!