What hasn't been brought into this discussion yet is that in about 3-5 years, those mics may need to be replaced. The tiny mics that work with
beltpack wireless systems are not invincible and while there are a great many threads on this site devoted to determining which is the most dependable, all of them can and will be broken by general use given enough time. Especially by the younger ones. By purchasing your own set, you need to also factor in and anticipate the repair costs of that set. I work in a high school
theatre and in the past 6 months we've lost one with 2-3 more starting to go out. We run a total of 14 beltpacks total of various make and use them about 7-8 times per year for various groups that request them.
Also, the FCC not too long ago rescinded a large portion of the bandwidth that wireless mics operate in, which made almost every single
theatre, church and school with microphones operating within the now illegal bandwidth have to replace their systems. I can't speak on the likelihood of something like that occurring again, but it would be a tremendous expense. The danger with eBay and Amazon is there's less of a guarantee that you're buying a setup that operates in the legal bandwidth too.
It sounds like you do this event once per year and the rest of the time you might have one or two things that crop up that it would be useful to have a set of bodypacks? My wife teaches elementary and does shows as well. The problems I've encountered is that unless you have someone who is rabidly ferocious about protecting and maintaining wireless mics in a primary school environment, stuff will go missing. People unfamiliar with the setup will lose mics, packs,
etc. and then you end up with a closet full of audio equipment that doesn't altogether not work together. I've trained her to be bitterly aggressive about protecting their hardware, but stuff happens.
If you were in a school and did 2-3 shows per year, I'd say buy as many mics as you think you can maintain or would need for the majority of your events. Listen to the advice about the frequencies. Reputable manufacturers and resellers will educate you on which models will fit your needs (especially if you plan on expanding in the future and/or supplementing with rental equipment). Having a small set of wireless that you own will be handy and save some money on rental when you need more for your big shows.
If this is a once a year deal though, I would probably say just stick with the rental as appealing as buying sounds (and especially if you're not having technical issues with renting). With renting, you're paying for that rental guy to guarantee that all those mics work in that environment at the right time and without failure. It's like insurance in a sense. If you buy, there's no one there in the middle of pre-show while your hundreds of kids are standing on
stage while
feedback is blasting through the
house because the
gain is too high on half the packs and the other half of the mics don't even work because they weren't tuned to the receivers right. If they don't work and they're rented, you
pick up the phone and it "should" be fixed. Assuming the renter is respectable.
I would definitely consider shopping around for rental companies though, especially given the Sony mic comment. On a professional scale, I don't think I've ever seen anyone using that make equipment. Names like
Shure,
Sennheiser and
Audio-Technica will be a
bit safer bet. A lot of their websites can also educate you on which frequencies will work in your area. If you buy 21 microphones but in a frequency band that only has 18 open bands in your area because there are TV stations using the rest, it's not going to work properly and that's not something that can be fixed easily.
The biggest piece of advice I can give you is to do your homework before you buy and don't buy on pressure of the deadline. If it's too close, rent this year and do more homework. My biggest pet peeve/general fear in life is when people in education or church settings spend money before they know what they need. It seems to happen so frequently with children-groups, schools,
etc. when a group with money decides they don't like how the production sounds and just starts buying stuff. I literally just went through this with my wife's school who has a PTA with $2k to burn and a bad taste in their mouth because they have crappy off-brand wireless mics that don't work through a brick wall. They were about to just start buying mics without even considering frequency issues when I got involved.
It keeps me awake at night...
Other questions that come to mind-
What type of
venue is this performed at?
What sort of audio equipment is provided by the
venue? (Speakers? Amps?
Mixer?)
What sort of staffing is provided by the
venue?
Do you have a technical director/audio guru-type person associated with your non-profit?