The last RB20 ECU I bought was $30
It will plug in, all you need to do is swap a couple of wires and you will have a single AFM ECU in the car. Simple as that.
If I can do it, you can do it.
www.paulr33.com
EDIT: R32 RB20 and RB26 ecu's all use the nistune type 2 board. So you are really at no disadvantage to Nistune an RB20 board. Later if you decide to go back to twins you can just move your Nistune to the RB26 ECU and swap the pins back, making it twin AFM.
Ummmmm simple? Yes.