Getting around Mandawa...that's easy! Your choices are...walk...maybe bicycle? The area of havelis is pretty small in my experience, so you don't have to worry about getting around. Unless of course you dislike walking. In which case, you should actually worry quite a bit.
You can hire a driver for relatively little in Delhi, and he'll take you wherever you'd like to go...for the most part. We had one great guy drive us all around Rajasthan for two weeks, and Mandawa was included as part of the trip. I don't know how else we would have gotten there. Maybe a bus...?