Can I get an all-in-one system (mikes+body packs+receiver), or will I get a better deal, or better equipment, if I do it a la carte?
That’s right. You’ll need 1x receiver, 2x transmitter, and 2x headset. Headset-transmitter is 1-1 and receiver-transmitter is 1-many.
The package for the one I posted is $329 (1x each): Shure BLX14/SM31 Headworn Wireless System with SM31FH Fitness Headset Microphone, J10
The extra transmitter goes for $139 and the headset for $99. That almost in your price range.
What you might do is look for well-cared for used ones, saving you that drive-off-the-lot cost. You could also probably walk into a Guitar Center and say “I want this and I can only spend $500. If you can do that right now, this will be your easiest sale all week.” I worked at GC ages ago and I loved these customers. I didn’t get the full margin on the sale, but the zero hassle made it free commission. Just don’t fall for the add on pitch (eg Monster Cables).
I’ll just re-caution about this kind of product. You almost always get what you pay for. That no name $80 set isn’t $329, but it will almost certainly be a complete waste of $80.
Btw, what kind of dance?