For such tourism concentrated city like Hue, there is not lack of methods of transportation to go around that you can easily catch a taxi, xe om, cyclo or you may hire yourselves a motorbike or bicycle at relatively low cost.
Like other Vietnamese cities, Hue is flooded with cyclos and motorbikes, as well as a few meter taxis. Taxi drivers are usually honest, but make sure they turn the meter on: trips start at 15,000 dong for the first 2km and tick upward at 11,500 dong/km. Some meters run incorrectly (showing up to 10 times the distance actually travelled), so ensure you have a rough idea of the distance to you destination. If the meter is running too quickly, at the destination pay an estimate of the fair price and insist on calling the police if the driver will not accept the estimated non-meter price. The driver will back down. A metered trip out see two tombs, with waiting time, should come to around 300,000 dong (US$18).
If you travel with a big group, you should arrange private car rental with hotels or any travel agents in Hue.
Hire a motorbike for 100,000 dong locally. Fuel costs 25000 Dong per litre. Correct as at Feb 20th 2013.Join the locals as they swarm across the bridges and along the main roads at a leisurely pace. If you're not familiar with motorbikes you may want to practice on smaller, less busy roads first. Gas stations can be found at some of the major intersections in the city - ask the person you are renting from to mark any they know on your map.Note that a map is a Foreign concept- nobody understands them, NOBODY. Make sure your motorbike comes with a helmet, as you can be fined otherwise. You can also buy helmets for 50,000-125,000 VND. Helmets priced at 50,000 will not offer much protection in a crash - these are sold so people can avoid fines more than to offer real protection.
New arrivals in Vietnam should familiarize themselves with the way traffic works in Hue. Take a motorbike taxi to get an idea how to fit into the traffic.
Cycling is also a good option, with plenty of bikes available from 25,000-30,000dong/day (March 2012).
For motorbike with driver, small hotels have connections to freelancers. You may be lucky to have an English speaking (a bit mumbled but knowledgeable) guide/driver/US army veteran for all 6 tombs (the 7th is inaccessible) including those locked and forgotten for lack of tourist interests plus three temples and the emperor's arena for one day and have extra time in the early afternoon for a beer and some Vietnamese do-it-yourself spring rolls and the famous Hue pancakes for just $10.
A cyclo is the local versions of the trishaw, with the passenger in front of the cyclist. Be prepared to haggle for reasonable prices as cyclo drivers tend to quote indiscriminately. It's a good idea to agree absolutely on your price before you go. Also make sure this is a return price, and not one-way. Of course, if you want to change your itinerary after you're already on the way, you should discuss how this might affect the agreed price with your cyclo driver right away. Otherwise, you may get a rude surprise when you arrive at your final destination, and the driver tries to charge you an exorbitant amount. Be aware that while most of the cyclo drivers in Hue are fair, and can be quite helpful, there are a few who are very unscrupulous. If you agree on the price as "100", make it very clear that you are agreeing on 100,000 Dong, and not 100 US dollars! Many cyclo drivers also act as pimps, and may offer you local women (starting at $10/hr).
Hue is quite compact, so you can reach most of the hotels, restaurants, and the Citadel easily on foot. Mr. Cu at Mandarin Cafe has prepared a free walking tour brochure & map. Make sure to stop by 24 Tran Cao Van St to pick up your free map (and enjoy some delicious banana pancakes). You'll need to arrange transportation to reach the emperors' tombs, though.