Construction in Panamá is not easy, much less in a town like El Valle, because there is not a specific store for building materials, and these have to be carried from the highway, raising the price. And this also goes for heavy equipment, and workers.
After you have completed your official documentation, make sure to sign a contract with a licensed contractor. Otherwise, you´ll end up paying a non programmed price.
It´s very advisable to have a Spanish-speaking Panamanian friend, or an attorney, to guide you though the process. Otherwise your experience could result in a nightmare.
Just don´t expect to pay $50,000 for your house to be built, if you are in a budget. Prices could vary way over that amount.