Ah yes...I assumed you meant a mouth harp (harmonica) - Completely differend ballgame (it did seems trang to suggest a lavalier). My Bad...
The Sennheiser is an affordable mic that works pretty well, and the DPA is a better mic that costs quite a bit more.
The Sennheiser MKE 1 and MKE 2 are about the same price as the DPA 4060 and are of equivalent quality.
It's only the cheapo ME 2 that is the cheap option (which I would not recommend for this use).
The MKE2 is about £190 at Canford but the DPA4060 is £285. I slightly prefer the DPA sound in most things but they can be a bit fragile.
That's the Gold series with the expensive connector for the 3000/5000 series radio mic pack.
The same mic with the connector for an EW pack is HERE at 195 pounds.
The basic MKE 2 5 with bare ends (which is what I priced) is now marked down to 158 pounds at Canford HERE.
Canford, of course, is far from the cheapest source (though those prices sound good to me compared to Aussie ones).
No criticism of the MKE2 (I haven't heard the MKE1 yet but have heard good things about it) and it's certainly considered a workhorse in the theatre sound industry (edited to add "along with Countryman"). However, the DPA is considered a little better for some applications and many's the time I've heard sound designers say "I'd like to have used a DPA but couldn't get the budget". Certainly, in the configurations and quantities used for big shows, the Sennheisers are about 30% cheaper.
Just as an aside, in the theatre world, the "tie mic" is rarely used on a tie. It's more likely to be up on the hairline or over an ear. Omnis are almost always used in preference to directional versions. On the other hand, in TV, where lavs ARE used on ties or lapels, for some reason Sony have a huge market penetration. The ECM77 or ECM88 have a huge segment of that market. I've used ECM77s in the hairline/over ear position and they worked well but have never managed to break the MKE2's popularity in the theatre--I guess it's a bit like the SM58 of the musical world..."I know I can get better but everyone knows how to EQ an MKE2" sort of thing.
However, just to offend your sensibilities, between sweat and enthusiastic dancing, the service live of lav mics in the theatre is very short. In the past few years, there's been a move to use very cheap Chinese mics. They're far from as good as the Sennheiser/DPA/Sony type but can sound okay with some EQ--and at under $30 a mic, they become a disposable like batteries instead of a capital item. Producers love them for that!
Things have moved on a bit since '86 and, while the MKE2 may have been ubiquitous 30 years ago but things have moved on. A good friend of mine is a multiple Tony and Olivier award winner (including this year) and I know he is a DPA fan. At the other end, for example a lot of touring shows (including ones designed by the aforementioned friend), the "cheapie" model has cut in. I'm not saying it's good but it's cheaper. Producers look at every expense and over 30 or 40 mics being changed every few weeks for a multi year run, the numbers get silly. Look at it this way. Forty mics at 200 pounds each is 8000 pounds every two weeks or 208,000 pounds per year. Change that to a 30 pound mic and the cost drops to 31,000...and, unfortunately, that's how the bean counters see it.
It's just like the move to digital desks from big Cadacs. The count every seat in FOH saved at the cost per performance and something that eats 8 seats instead of 16 saves hundreds of thousands (or even millions) over the course of a run.
Of course we haven't discussed Countryman yet. That's the other big player in live theatre!
By the way, do I remember your name from Sennheiser many years ago? I seem to recall getting a quote once from somebody with a similar name but selecting a different manufacturer. This was back in my TV days when we were equipping several studios and some ENG crews.