Replacing the front brake pads on an Altima isn't that difficult of a DIY job and only requires a few common tools. You can save a ton of money by doing this procedure yourself, just be sure to torque all the bolts to the proper specifications.
The front pads can last anywhere from 30 to over 75k miles depending on how you drive and your climate. For new pads, I'd recommend the Wearever ceramic pads from Advance Auto Parts that cost about $46 for a set.
Here's the guide -
Cheers, Paul