Yes, many choices on eBay, Amazon, elsewhere.
Direct links to eBay are supposedly not allowed on OGR per terms-of-use but you can easily find many sellers of the above module for about $3 with free-shipping from Asia.
Most of these low cost modules operate on, say, 12V DC voltage. And have a relay which can switch 5 or more Amps of AC current so more than suitable to control one or more O-gauge accessories.
For what you stated, you want a module that is "triggerable" since you press a momentary button to start the action. That is, you apply a momentary voltage via the pushbutton to start the action (30 seconds of power in your case). I even set this module to 30 seconds to illustrate. This particular module even lets you define what the pushbutton does. For example, when pressing the button you can:
1) start a single 30 second interval (pressing button again while active does nothing)
2) start-or-restart the 30 second interval (pressing the button again while active extends another 30 seconds)
3) reset the interval (pressing button while active stops the 30 second interval).
There are more sophisticated timer modules for a few dollar more. For example triggering the module can turn on the relay for 30 seconds (or whatever you program), then turn off for 5 seconds (or whatever you program), then repeat this ON-OFF cycle 7 times (or whatever you program). All in response to a single button press!
You get the 12V DC to operate these module from a 12V DC wall-wart adapter - about $2-3 on eBay free shipping from Asia.
Or you can get an AC-to-DC converter module which will generate 12V DC from train transformer Accessory Voltage (14-16V AC or even 18V AC command track voltage) also for about $2-3 on eBay free shipping. One 12V DC adapter or AC-to-DC regulator module can power a dozen or more timer modules.
Any low-cost momentary pushbutton switch can function as the trigger. If using the above timer, the wiring would look like this for 3 accessories. The current flowing in the 12V DC wiring on the left is modest (well less than 1 Amp) so less expensive thinner wiring can be used - 24 AWG for example. There is probably existing Accessory Bus wiring around the layout. Some accessories can use for than 1 Amp so use suitably sized wiring - I'd think 18 AWG would be sufficient for most applications.
If you want to "over-ride" the timer module and have a toggle switch that simply turns on the accessory all the time, place the toggle switch across the 2 relay screw-terminals (labeled NO and Com) on the right side of the timer module.
And the way these modules are triggered, you can use a 5-cent diode with a pushbutton so that you can have individual buttons triggering one timer module/accessory...while having an "ALL" pushbutton that triggers all timer modules at once.
I think I'll stop now. 
