Years ago, I started with a wall wart as my PSU. It was from Jameco, as I remember, branded by Motorola, and provided 5V DC, 12V DC and -12V DC. It was very cheap, but the specific unit is no longer available. It served me for more than an decade, and I still use it.
I suggest you look at:
Jameco.com
MPJA.com
for something that will meet your needs or start with a PC power supply, for which there an innumerable posts on the Internet.
This is certainly one situation when posting your location would help us give more specific advice.
John