$75 canadian for the Sony EX-71... they're worth the money only if you can't afford the cost of the Shure E2c headphones. Also, don't buy plugs unless they're by a reputable brand and they look to have excellent build quality. If the plug is gigantic (like the koss phones), chances are, they won't sound very good.
That said, the headphones you buy should depend entirely on the environment you're in.
If it's a noisy place, get earplugs for sure. DJ cans work as well but I avoid them at all costs. They're terrible for creating an accurate representation of what you're hearing - particularly with the way dj cans tend to over-emphasize the treble and bass.
If you need noise to get in, i'd reccomend open air can-style headphones. Street style phones tend to have really ****ty quality 👎. Check the Grado sr60. These are undoubtedly THE BEST headphones on the market for under $100. Absolutely nothing comes close other than the Shure e2c's which cost $99.
Another option you have is a cmoy amplifier. These things are cheap as hell to build yourself and new ones can be bought on ebay for under $80. They're pretty compact and can fit into an altoids tin. The sound difference you'll get with a good amplifier is like night and day. They'll make even cheap headphones sound damn good. They do this by allowing the phones to utilize the full frequency spectrum better than the amp on your mp3 player will allow.
All of the headphones I mentioned minus the Sony EX-71 can be bought at
www.headphone.com - easily the best place to buy your headphone related equipment 👍