Taxis are the quickest alternative for getting to and from the airport. The current going rate for the 30- to 45-minute journey is around (Bs)45—use a taxi from the rank and you won't be overcharged. Minibuses also service the airport. The cost is approximately (Bs)5, but it's rather a rough introduction to La Paz.
Within the city, taxis and trufis (shared taxis), identifiable from the destination sign lodged in the windshield, are cheap and plentiful. Expect to pay less than (Bs)6 for most trips within the city center. Newer radio taxis, identified by the illuminated sign on the roof, are the safest option for tourists. Rates are fixed at (Bs)6 to (Bs)20, depending on the length of your journey. Cheaper are micros, 12-seat minivans that travel roughly the same bus routes. They're quicker and more comfortable, especially if you get the front seat. Listen carefully before you board, as destinations are shouted out the window as the vehicles roll through the city. Better yet, ask a local to help you locate the right one.
Because La Paz is so compact, visiting the city's main sights would seem easy; however, add time if you're walking for climbing the hills and taking frequent breaks to assuage the effects of the altitude. You'll need a couple of days for a thorough exploration, but don't worry about getting lost—if you do, just go down the hill and you'll reach the main avenue eventually.