Cost of land not considered but you're looking at $10-$30K for site prep and foundation and anywhere from $125K-$200K for the building plus finishing. Prices will go up when you add in utility connections depending on what is available locally, need for private sewerage plus engineering studies, plus applicable labor & permits. There are alot of variables, you should Google modular homes and then research which companies have experience in the town as well as builders in and around the area who have established business relationships with the town. You could also contact a real estate professional to ask them to find properties that are of like type that interest you and find out who they used and their experience and satisfaction with the builder & modular company.
Hope that helps,