In general, I prefer to DM. As a result, i would only pay to play under one of the top top DMs in the world, and then mostly to see what they do differently in order to pick up some tips and techniques.
As far as being paid to DM, I think you underestimate my charges. If I'm being paid, then it's a job, and I'll treat it as such. This means being fully prepared, arriving on time, being polite and professional, and basically doing everything in my power to ensure the group have a good time... and it means charging real money for my services.
My prices would most likely be the equivalent of $30 per hour for a regular session (half that if I can include 'prep time' as part of my billable hours), or $150 for a half-day game session (probably about 6 hours gameplay). Those numbers can come down if I can do sufficient business to make this my primary means of employment... but since I wouldn't be able to, you pay a premium for cutting into my 'leisure time'. This is a far cry from paying 'a few bucks each' for the priviledge.
Based on that, I cannot see any group paying for a regular game. There are too many DMs, and too many really good DMs, offering their services for free, to make that arrangement work. I can see the occasional group wanting a one-shot session, perhaps as a birthday celebration, or because the old gang are back together for one day only, or whatever... but the practical question is then how one would go about advertising the service?
However, there is one other way I can see this working, and it was mentioned by the OP...
If I'm running a game store, then I might well consider hiring a DM for a day every few months to run demo games for new players. The idea here is to get someone who runs a really good game, and more importantly a really good demo game, and thus suck newcomers into the hobby. As we all know, the single best advert for D&D is to play it with a really solid group, so there it is.
More to the point, I might look for the ability to run a really good demo game amongst the people I would be hiring anyway, and try to get them to do the job for me, since hiring a professional DM at $150 every few months is likely more than my store could afford to spend.
In that instance, though, my expectation is that it's the game store, rather than the players, who pay for the DM, and that it is done as part of their 'advertising budget' rather than for any other reason.