Did this couple of months ago. There's a standard 10-14 day "track" sold on a Vietnam Air ticket - Saigon - HoiAn/Hue - Hanoi/Halong Bay or the other way around. The ticket is cheap. If you call Vietnam ailines, they'll give you their "prefered" agents. I also prefered one of them, because they are very knowledgable, get you cheaper visas (the cheapest is via in-Vietnam travel agent), very friendly and have broshures with 10-12 day itenerary, which is OK to follow on your own. I got partial advise from them on hotels. You get very good quality for 30U$, unles it's big, or "guidebook" hotel. Just travel agents know only big hotels and Lonely Planet quote pushes prices up as usual. Car: 20-30 US/day. Big boat 10 US/day. Locals bargain hard lowering the price to more acceptable (sometimes still high) levels only when you leave. Sometimes the selers are more than reasonable.
I got my first lifetime experience in amazinng 8 US/night 40m.sq. clean new TV aircon hot-water high-ceiling room with shampoo/ toothbrush/ slippers

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If you don't want to do the "track", you can go to one of the three "points", explore the locality, go mountain trekking, river/beach fun, taste good street food, talk to nice local people... It won't be boring either.