I agree with the above posters that Miguel is a high-end Guide. His services are amongst the most expensive, but that is because he is one of the best (in my opinion hands-down the best) Guides in Mendoza. His contacts are second to none, and will be able to get you into places that most run of the mill guides will not. To put things in perspective, being one of the most expensive doesn't mean that his cost is anywhere near unreasonable. When you factor in the price of what he charges to the overall trip expense, its a drop in the Ocean and what you get for hiring a caliber guide repays itself many times over.
Also, please note that you need to work out the math before concluding that a Guide that quotes you in US$ cash is more expensive than one that quotes you in Pesos. Look into issues of forms of payment and what the currency markets are like. Most times, once you do the arithmetic you will realize that the Peso price quoted is not too far from the US$ cash that Miguel and other top guides charge. It is standard industry practice to have guides charge for their services in US$ Cash, that is the norms for all the good guides here in Buenos Aires.
As a Argentine that goes to Mendoza some 4-5 times per year, I think that saving a few bucks on not going with anything but the best of a Guide is definitely not a good choice, but it is of course up to each individual traveler to do his/her own homework and make the final decision.