I think its the cheapest safety earmuff + stereo and fastest to do build or rebuild if needed.
It requires no soldering or drilling. This is my cutdown version of safety ear protectors with stereo speaker inserts from the following fabulous instructables.

Hearing Protection W/Tunes: Earmuff Modification By jdchicker in Circuits.

How to Make Bluetooth Music-enableHearing Protection By wemcdonald in Circuits Wireless

Supplies

Safety Earmuffs
Stanley knife
Double sided tape/foam
A pair of old stereo headphones / ear plugs
Shoe glue or Neoprene glue.

Step 1: Choose Your Speakers.

Probably the most important part is the choice of headphones/earplugs - I used stereo earplug type from old phone - they are free and are usually left in the drawer as I don't use them -I don't like pulling them in and out of my ear and they are a little uncomfortable for me - but we will be sticking them inside the earmuff cavity so that is no longer a problem.
Some speaker sets have a microphone / volume dial which is a bonus. If you want better/louder sound you could opt for standard headphone set as long as they fit in the cavity, and you may need to partially dismount the headphone casing to access just the speakers. Just try and leave the wiring intact to save doing solder work for the install . You can always just do a dry run to test before gluing everything in.

Step 2: Step 1. Prepare the Earmuff Casing

Pull apart the padding that is connected to the ear protection hard casing, you only need to separate it enough to slide your speakers into the cup area.
Remove the mouse padding in the earmuff cup and cut a small space in the foam to suit your headphone. With the stanley knife cut a small channel cut on the inner rim where the padding gets glued. You can use a file or dremel but be careful no to make it to big. This serves as a knot stop for your wiring - so make it just big enough for the headphone wire.

Step 3: Step2 Insert the Speakers.

Put a knot in the headphone wire about 5cm from the speaker/earplug - do a dry run to make sure you knot catches in the groove whilst the speaker is in position - once your happy with that use double sided tape to position the headphones.
A spongey double sided type is best to position and stick your headphones. Replace insulation foam around the earplug in the hard casing, running the cable through the cutaway. Put some shoe glue around the hard casing and put the foam in place again, lift it up so that the glue then covers both pieces - make sure the wire also gets a glue coating as this will help seal the padding and reinforce your wires. Once the glue has setup squeeze the padding and hard case together sandwiching your wire. You can clamp the hardcases together and leave them for a few hours to make sure the glue is set and makes a good seal.

Step 4: Conclusion.

I find these work prettty well - the earplug speakers are loud enough because they are isolated within the earmuff cavity. I can hear them well when I run the weed whacker or mow the lawn.
Is it great top quality sound ? - no, but maybe normal headphone speaker set would be better. The cable can get a little in the way whilst working so beware - I usually sling it over my back and put my phone or player in my rear pocket, or in my shirt pocket for the ride on mower.