Tours to Laos in March are not very popular. A serious heat wave begins, the water in the rivers drops, many small rivulets dry up. It is cooler in the mountains, but not everywhere there is tourist infrastructure.
Of course, you can go to Luangnamthu, where you will quite successfully get acquainted with local customs and tribes. Or limit yourself to the capital, Vientiane. The developed city of Luang Prabang also welcomes guests at this time. Prices for vacations in Laos in March are falling.
You can find excursion options for 900-1000 USD, especially if you count on hot tours. In the end, vacation in Laos in spring, especially early spring, is limited to excursions, excluding most options for sports. We don't recommend going to Ponsavan at this time; there's little shade and it's hot.
Prices for tours to Laos in March range around 1500-1600 USD for sightseeing programs in the central cities. If you don't know which cities and resorts you can go to for your budget, use the tripmydream service. It will find the most cost-effective tours to Laos in spring.