For starters, don’t even THINK about $10-30 mics. They all stink.
The “industry standard” for live performances is generally the veteran Shure SM58 dynamic microphone, which is compatable with practically any piece of equipment on the planet, and retails at about $99. It can routinely be found at a discount as part of package deals, which also include a stand, XLR cable, or more often several microphones with stands, cables and connectors.
For buying gear the best online retailers are Musician’s Friend (musiciansfriend.com), Samash (samash.com) and Sweetwater (google them). They all have price-matching guarantees, so the prices will be more or less constant. The best regular physical stores are the Samash retail outlets (google them too).
Other companies make similar products, like the Electrovoice series, but the Shure SM58 is pretty much the standard. (if the president uses them,so can you!)
Good luck!