There are several rental agencies at the airport. You will get a cheaper rate if you arrange it over the internet than if you wait till you get here. You will not need the car once you are at our house. Be sure to have pesos for tolls that are quite expensive.
We have a private driver we use who can pick you up from the airport and bring you right to our front door. He has a very nice car or van for larger groups. It is $165 one way. This sounds like a lot, but for larger groups it is the best option and it is very convenient.
Rather than taking 2 seperate buses and have to change bus stations in Cuernavaca, I recommend taking a taxi from directly in front of the airport terminal to the Tasquena Bus Station. This is about a 30 minute drive and costs around 100 pesos (this price is at least a year old.) The taxis are well organized so buy your taxi ticket right inside the terminal or coach station so there is no gouging. You will then take a luxury coach directly to Taxco which will take about 2.5 hours. The bus company is www.estrellaoro.com.mx. You can book and pay on-line and may wish to book your return too. Once in Taxco a taxi can take you to Casa de las Palmas for 20 pesos.
Address: Casa de las Palmas, #13 Calle Guadalupe (enfrente Casa Piedras), Taxco , Mexico