Highfigh is right. If you’re talking about a permanent installation, this kind of thing requires a professional pro-audio installation company that is familiar with what equipment can reliably be used and permanently located outdoors. This includes special wiring suitable for direct burial, sunlight exposure, etc.
Don’t expect to do this on the cheap, especially since you’re talking about four stand-alone systems. For instance, good-quality wireless mic rigs cost in the neighborhood of $4-500 each. Cheaper one typically have all kinds of shortcomings and are generally a waste of money.
Now, if you’re talking about something portable that can be set up and taken down as needed, that’s a whole different thing and could be done cheaper than a permanent installation. But even then a professional should be consulted to make recommendations based on all kinds of factors, such as where the audience is (e.g. isolated to a specific location, or spread all around arena perimeter?) and all kinds of other things an amateur can’t even imagine.
Regards,
Wayne A. Pflughaupt