If you do end up finding a way to estimate the total cost of wheelbuilding,
718 Cyclery in Brooklyn does free classes once a month. It's not the most convenient shop for you, but they seem to know their adventure biking stuff, and could probably give you tips and ideas (and maybe an estimate) for specific 650b wheels that would fit your Jari! I've been looking at Salsa's and All-Citys with them, and it seems like a great independent shop, despite the location.