What is the easiest way I can power multiple dc motors at the same time?
The obvious place to start is eBay. You don't say what voltage you need, but let's say you want 24 volts. Search on "24 VDC power supply" and look at what's available. I gave it a try and found several in the 20A (480 watts) range for about $50.

And no, 1kW is not ordinarily hobbyist level.