Given the modular nature of this project, there is no requirement to use a transformer; all that is needed is a stable +/- voltage somewhere in the range of +/- 8-24V (depending on your output requirements). A transformer is the obvious simple way to do this, but there are others.

The simplest (most ghetto) way is to use two wall warts. This will give you the dual voltages needed, although it is probably a bit limited in current, depending on what wall warts you have on hand. The biggest downside is that it is ugly and clunky.

I am looking into something like this. In theory I can use two of them in the same configuration as the wall warts, and get a split rail. I am not sure on the details of this, though; if anyone has any experience doing this or has a link to somewhere that tells the specifics of what needs to be done, I would be very grateful.

Any other suggestions on the best way to get a +/- split rail supply on the cheap would be very much appreciated.

Cheers