Howto start in the multirotor world

There are many friends asking what is the cheapest way to enter in the multi rotor world.

Let's do some numbers based on a quadcopter running multiwii firmware:

1 x Arduino Pro Mini (18,95$)
1 x FTDI programmer (14,95$)
(Sparkfun shipment = 8.94$)
1 x WiiMotionPlus (19.99$)
1 x Nunchuk (19.99$)
1 x Board for connecting all the multiwii stuff (14,95$ + shipment 3$)

You need a radio: the cheap turnigy radio from hobbyking (53,79$ + shipment 17$)

You also need a charger for your batteries:
1 x charger + 1 x power supply (22.99 + 9.99 = 32.98$)

Some common materials for the center plates and arms:
1 x G10 center plate (7$ + shipment 8.46$)
1 x aluminum square tube 12x10mm, 2,82$

Now, you can choose the size of your quadcopter:

• Let's imagine you want to build a tiny size quadcopter (25cm motor to motor)
  4 x Motors, Turnigy 1811-2000 (31.96$)
  4 x ESC, Plush 6A (29.64$)
  1 x Battery, Rhino 610mah (5.29$)
  (Hobbyking shipment = 9.99$)
  4 x Props, 3-blade 5x3 CW and CCW (3.22$ + shipment 3.56$)
  
• Maybe you want a medium size quadcopter (40cm motor to motor)
  4 x Motors, KDA 20-26M (45,24$)
  4 x ESC, 18A (44,2$)
  1 x Battery, 2200 mah (16,48$)
  4 x Props, 8x4 CW and CCW (4.56$)
  (Hobbyking shipment = 14.99$)
  
• Or you need more power and want a big size quadcopter (60cm motor to motor)
  4 x Motors, KDA 20-22L (51.52$)
  4 x ESC, Plush 25A (47.24$)
  1 x Battery, 3000 mah (24.32$)
  4 x Props, 10x6 (2.93$)
  (Hobbyking shipment 17.95$)
  

TOTAL Tiny = 306.48$ (215 euros)
TOTAL Medium = 348.29$ (245 euros)
TOTAL Big = 366.78$ (258 euros)

Of course, there are expensive alternatives like replacing the arduino pro mini with a flyduino, replacing the WMP+/Nunchunk with Jussi's FreeFlighImu or using the Diydrones APM/Oilpan.

Note1:
All conversions have been made using dolar-euro rate at 1.42

Note2:
Some users point me to the OpenPilot control board that is also in the 100$ range.