I've done some research on everything, and I found some very interesting links:

Quad:

This is where I got the idea on how to build the quad, here and here.

I'm building the same frame but with DIY electronics.

As about the electronics of the quad here is a good article explaining how everything works. But I also found much easier to read & hack code here. It might need some improvements which I think are very easy to implement on such clean code.

Transmitter:

The main idea is here and I also found this guy doing almost what I'm doing (with a much more decent quad, but on the 200$ price tag).

What we need for the transmitter is just the case WITH the pots. You might be able to get it free (ask for broken transmitters on hobby shops). If you can't find, just buy the pots and put them on a piece of wood (be careful not to buy just joystick pots but the "rc controller-like pots" like the guy in the second link explains. It will be much easier to fly).