Bagan is one of the most beautiful religious sites in Myanmar. It's also one of the most iconic, and a trip to Myanmar can't be considered complete unless Bagan is part of the itinerary. It's best to visit Bagan while the weather is cool enough to ride bikes among the temples, but not so cool that the weather turns against you. I visited Myanmar at the height of summer, and spent the entire trip coated in sweat and temple grime.
Still, I had a great time exploring this town on my own. The hotels are more expensive than other parts of Myanmar, but if you stay in Nyaung-U, a region just outside the area with the temples, you can find something affordable. I think I paid around $12 American per night at my hotel, and got my own room, but I had a communal bathroom.
If you go, I'd recommend staying at least two full days and three nights, which will give you enough time to see most of the temples, as well as a sunrise and a sunset. Beautiful!