One option is to use PHP function empty() and the AND / && operator to build your if check to be certain that all of the required parameters are present.
if (
! empty( $type_search ) &&
! empty( $area_search ) &&
! empty( $prezzo_search ) &&
) {
// your ocde
}
P.s. type and area could be an excellent opportunity to use custom taxonomies and terms instead of post meta, if they can only have one or more predifned values and they are used to group posts together. Using custom taxonomies can provide you better performance, more on this for example here, https://tomjn.com/2016/12/05/post-meta-abuse/ (not written by me).