they receive much praise and obviously do a great job. my question is, does anyone know how much more, or less, it may cost using them (or any travel agent), than making reservations by yourself? i am about ready to "sign-up" with wow!,but a little reluctant......

Advantages booking direct not always provides the best deal, depends on time of the year, occupancy, situation of the TA or Hotels / Flights. Anyway there shouldn´t be HUGE diffences .

We used Wow Argintina and Cintia was able to book us for less cost than we would have spent via the internet. Additionally, they were a great resource. My husband was interested in yacht clubs, her husband Matio faxed us information the next day.
Wow booked our BA hotel and side trip to Iguazzu, a tango show and picked us up from the airport and gave us a private tour.

We used Cintia for our trip to Argentina this past December. In terms of costs it varied. For some things she could get a better rate, for others the same rate and then I got a better rate for 1 hotel. She is a tremendous resource and very helpful.

I used Wow! Argentina for my trip to Iguazu last Spring. Cintia was very helpful and offered a lot of insights about Buenos Aires and Iguazu. She booked us a wonderful room at the Sheraton. I don't know that using her company cost much more or less, but it sure was a lot more convenient.