it is the organ itself that I need for, you know, less then $40-50
I have no idea the scale you are talking (not familiar with the piece you are talking about), but if you live in the States, you might try any of the big box Hobby/Craft stores... Michael's, Hobby Lobby, A.C.Moore... If memory serves, all three have a doll house section.. Not big, but it's there. I have no idea if they'll have a piano, or how much, but they might have what you want..
The other option might be to make the keyboard out of Strip Styrene... Lay down flat pieces for the white keys, and maybe really small square pieces for the black keys... You could use balsa wood to build it on (and/or make a surround for it), or plasticard... If you can build the pipe portion, you should have enough skill to do the keys...
Caz