The purpose is living there for about a year to see if a permanent move can be feasible,
if I really like the atmosphere, infrastructure etc. I intend to start a business partnership there, but at least not until I spend about 6 months in and around Bali getting really acclimatized to the bureaucracy, culture, etc. So it will be purely touristic, let me know if you are interested...
Third party services charge like 20 USD / head, which to me seems like a way to just make some extra cash off visitors, as it is literally a very simple standard letter + address of the inviter...