By plane
You can fly to Bagan from Yangon on Air Mandalay (http://www.airmandalay.com), Air Bagan (http://www.airbagan.com), Asian Wings (http://www.asianwingsair.com) or Myanmar Airways (http://www.mot.gov.mm/ma/...)] for US$ 93. Air Mandalay and Air Bagan also fly from Mandalay. From the airport to New Bagan, it takes about 15-20 minutes by car, and usually this will cost around 7000-10000 kyat. Most midrange and luxury hotels will provide free pickup from the airport.
By train
Overnight trains run daily from Yangon, departing at about 4:00 pm and arriving in Bagan at about 9:00 am the following day, at prices ranging from a few thousand Kyat a few dollars in second class, to US$50 for a "luxury" sleeper.
There is a direct train service running from Mandalay to Bagan with two departures daily. Tickets are available directly at the railway station and cost about US$6 one way. The journey takes about seven hours.
Most train routes in Myanmar are fairly nice, however when going on the Mandalay-Bagan route expect the train to be incredibly crowded. You will also have limited room to store your stuff, as well as cramped uncomfortable sitting conditions. The night train to Bagan has lots of room and feet space in the 1st class carriage US$10.