No one here is saying that the OP should go out and buy, say, a
Sennheiser 5000 series set. The
point we're trying to emphasize is "buy once, cry once." In my experience, just because you pay a small(er) amount for something now does not guarantee that you will only spend that amount on said
purchase. By that I mean, say you buy a $150 wireless set (in keeping with the theme of the thread) from Nady or Behringer. Chances are that in a year, you'll spend another $150 to replace it because it broke (and not always from user abuse). It may even be DOA, and you have to buy another one. Now you're over $300, closer to $400 in the hole, and adjusting for inflation, you could have spent the same amount in the beginning on a nicer piece of gear and have it work for years.
Based on this, renting when you need to is a perfect way of getting nice gear and not spending too much. Buying used is another great way. I had a POS amp die on me recently that I'd bought because it was cheap. Now I'm going to get a used XTi to replace it for near the same amount as I paid new for the dead one. Make nice with the local rental houses and they might even give you a nice discount on rentals. That being said, yes, some things it's cheaper to
purchase rather than rent all the time. But wireless mics aren't something one should skimp on; they are many times the weakest link in the signal chain.
As to your
point about "a good engineer can make any equipment sound good," you're right to a certain extend. In my eyes however, this is not a good justification, as it will lead to "Oh, they're good enough to make due with whatever we give them," which winds up being cheap gear that breaks in a month or two, or worse, fails during a show. I've had both happen because of that attitude from a few employers.
As I said, we're not saying that if you need an upgrade that you should wait until you can afford a DigiDesign
Venue, or L'
Acoustics V-Dosc, but that doesn't mean you should just skimp and buy a Eurodesk with matching Behringer speakers because "It's a good deal and we have no budget." Hold a fundraiser (or bake sale, I like those) to at least add a little
bit more cash to the pot. The key here is finding a good balance between cheap and reliable. Don't just go to the bottom of the pile because the price is right.
The
point I'm trying to make, and trying to get back on topic, rent what you need. You should be able to get a decent deal on
Shure SLX series from a rental
house when you need them. I strongly recommend this route because the OP says they're going to put it away after its one use to use later on other shows. I would be leery trusting either of those two brands that long. I recommend this route because I've been on both sides of the equation, and have been bitten by these sort of problems more than once.
I don't mean to single anyone out in this post, and I mean no offense, I just wanted to explain my position. I don't believe that throwing money at a problem will make it magically go away, but you do get what you pay for. Some of us have been in these positions before more than once and know how frustrating it is, just so you don't think we're all Monday morning quarterbacks.