I just came back from Mendoza with my husband and we loved it. We stayed in Maipu which is at 30 min in bus from mendoza city and for us was the best as we had enough of cities and wanted to relax in the countryside. We arrive by bus and it was very simple to take an urban bus from Mendoza to Maipu central park (it costs like $2 ar), the owners of the posada picked us there.
We stayed at Posada Cavieres, attended by the owners, a nice couple with a beautiful house, very kind with an attention that made me feel I was visiting friends. We rented bikes with them one day, they tshow us a route were you can get a wonderful view from the andes and the wines fields while visiting some wineries and they offer transportation service as well if you need it (you can even take in their car your bikes so you will make only one way and wont have to ride drunk!!) I also recommnend their wines and Alina's (the owner) pizza
We went to Trapiche wineries which is one of the biggest in the ocuntry and it was amazing, it cost us $20 ar, it was am ore commercial tour but very interesting and the place is an old building, very beautiful it really worths to get there, but the best wine tour we had was at Bodegas la Rural they have a Wine Museum...the guide there was the most professional and in second place the place is also very interesting. It was free. We also visited Vistandes and Carinae, both newest but also professionals with very good wine.
Here is the link of Cavieres, you will find all the info there about wineries to go and telephones, the owners of cavieres can make you the reservation because for some places you need to book few hours before, but most of them cost between $10 and $20 Ar. I believe there are some wineries more expensive, but I was very happy with what we got.
Enjoy Mendoza...I really loved this place.