I know that sm 58 are an industry standard but these days their price have gone through the ruff here in the UK so when we went on buying new mics we looked are other cheaper alternative and here's what we found
we got a couple of EV CO9 for half the price of the 58 and they are great!
In fact they are closer sound wise to the Beta 58 the sound is very crisp and well define truly good
construction is rugged and I really don't see why I would spend £50 more on a SM58 when you can get a similar or either better mic for much cheaper

Try on line shop.
Beta 58s retail here in Australia for about A $320 ...I bought 4 In Japan for our band for A$127 a pop.
Even the Rode nt 1a here $400 but there $175   crazy stuff.
When ever I go there get swamped with orders from mates ...hey can you pick up a .....4 me while there.

A friend of mine got a new shure sm58 with case and mic clip in singapore for $35AU equivalent. That's like $25US or thereabouts. But that was extra cheap because it was the last one in the shop and it was on display. I think the normal price was like $90AU.

Personally, wouldn't mind even buying sm58 second hand if price was an issue cos they are sooo rugged and the insides are so simple that nothing can really go wrong unless components are missing or the wire inside is detached. It really is a great mic, sound wise... there are a few cheaper mics that sound the same but this thing is durable, multiple 5 foot drops on solid concrete and sounds the same as a new one, no buzz, no hiss nothing.

there are a lot of mics that are as good or better than the shure sm58 or beta 58.  Used mics are ok just test them out before you buy them.. plug em in and move them around all directions ,.,lightly shake em.

 We use Sennheiser mics now. A little more money than the 58's but the sound quality is superb.

It depends what you want to use the mic for, if it's gigging then the trusty old sm58 is great.  I always say try before you buy.
When I formed my first band in the early eighties, I tested out the Sm 58 and audio technics equivalent ( don't know if they make them any more), well I couldn't tell the difference in sound quality or build quality, the Audio technics was half the price, needless to say I bought the audio technica, and I still have them, they are still great mics and have stood the test of time.

If however your going to use them in the studio, that is a different ball game all together, but you don't need a rugged mic for studio, just one that does the job, I love my AKG 1000s condenser mic (can work off a 9 volt battery), it's very versatile I can use it for anything, plus I have a SM57, another very versatile mic.

There is so much on the market now it's hard to pick one.

If you have the opportunity, go to your local music store and try some out.

I forgot about this..  I was jamming with some friends and they had very good mic sounds.. come to find out they were using some of my old favorites  .. buyer dynamics

http://www.beyerdynamic.de/international/

I didn't look at the prices so not sure how much they are.