AC adjustable timer, motion sensor timer

Heres the setup:

1. I have standard household current (110v, 15 amp, AC) entering into a device.
2. A momentary pushbutton switch is pressed.
3. This feeds a current to a standard receptacle outlet, activating a light.
4. The switch is released.
5. Power is cut off to the light.

Here is what I want to accomplish:

1. When the pushbutton switch is released, the current flow to the receptacle continues for an adjustable amount of time (ex: 4 seconds to 10 minutes).

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Motion sensors from any hardware store do this same thing. They have a switch to select 4 seconds, 10 minutes, or 20 minute activation. They are typically hooked up to a light socket or sold individually for a little as $10. I have found "AC Relay timers" on industrial supply sites, but they cost upwards of $50 and are very large units themselves. I don't need motion of proximity sensor capability since the device it switch activated. I simply need to keep current flowing for a length of time after the momentary switch is released.

I guess, as a last resort, I could buy a motion sensor, disassemble it, and somehow bridge the motion sensor part. However, I'm hoping to accomplish this with premade unit of some kind, and for under $10 (since ill be making large quantities.)

So, does anyone have any ideas of suggestions?

Thanks

-Matt