Play sound file with 1 button press through PA system

I really don't know where to go for answers, but while googling, I found some old threads on this site the lead me to believe that someone here might be able to point me in the right direction.

I'm trying to put together a system that will have a giant button, and when pressed it will play an audio file (mp3 or wav, doesn't really matter) through a PA system on my race car.

The current system I have is a dixie air horn and a staples easy button. There are 2 problems with this setup: 1) You have to hold the button down the entire time it plays, and 2) It's not loud enough sometimes.

It has to be robust enough to withstand off road racing, and loud enough to be heard in an outdoor arena environment. So I was thinking about just setting up a small PA amp hooked to a 100w horn speaker, and run some device to it....that device is what I'm not sure about. I don't think any commercial mp3 player will fit the bill. It would be really awesome if I could hack up another staples easy button to embed a controller with an audio jack for output.

I saw this, and maybe this would work, but not sure if there is a better solution out there: https://www.invitebyvoice.com/push-button-sound-module.html

So, does anyone have any ideas on how to easily and cheaply accomplish this?

Oh, and here's a shot of us in action with the current setup for reference (yes, we are in the Jeep):
https://www.youtube.com/watch?feature=player_detailpage&v=jrFZSFW6ZbM#t=432s

A fairly simple idea which occurs to me is a timer circuit which is started by a simple push-button. The timer, which can be adjustable, energises a relay, the contacts of which switch on the power to a suitable audio device for a period determined by the timer.

As far as I know there is no mp3 player which can be switched on directly into the play mode, so that suggests the use of a cassette player. The simpler ones can be left in the Play condition when switched off, and will start to play once power is again switched on.

Check out Sparkfun's MP3 Trigger. https://www.sparkfun.com/products/11029

You can also use the Arduino with their MP3 Player Shield and the MP3 player shield control example sketch. https://www.sparkfun.com/products/10628

I used their Arduino Pro 8Mhz/3.3v with the MP3 VS1053 breakout (could also use the VS1033 breakout, cheaper), and SD card breakout with the MP3 Player Shield Control sketch. Worked fine.

Hope this helps.
Randy