Of course you could argue that the point of a rythm section is to play the rythm and the lead instruments and voice should learn to stay in time. It all depends on whether you are the vocalist or the bass guitarist (or drummer). Some shanty singers are awful, and shanties are worksongs that have to have that pulling rythm just so.

If you want to save half the price of a Shure SM58, try an AKG D880. I got my daughter a Sony Shure copy for GBP 17.50 (a heavily discounted new Shure SM58 is GBP 80) and after a little soldering it worked well, not a smooth as an SM58 but passable. I also got her an old AKG D190E (takes you back, eh?) for GBP 25. Mikes, like power amps, should be heavy or they sound tinny.