How do I qualify as a rentista or pensioner for permanent residency and what does it cost?

The IGM lists the rentista (a person living on independent means) or pensioner as a route to permanent residency: permanent monthly income from abroad of at least US$1,250, plus US$300 for each dependant; no guarantor is required;… income must be re-evidenced every 5 years. The one-off cost is US$400, plus the US$25 application fee and the general documents.