20. Is there a limit on the amount a candidate can contribute to their own election campaign?

Código Electoral de la República de Panamá
Artículo 248: 
Ninguna nómina de candidatos a cargo de elección popular podrá recibir de una sola fuente contribuciones privadas que excedan los siguientes porcentajes sobre sus respectivos topes de gastos:
1. Las presidenciales, 3 %.
2. Las de diputados, incluyendo a los del Parlamento Centroamericano, los alcaldes, concejales y representantes de corregimiento, 25 %.
Para aplicar este tope, la nómina restará lo que financie con recursos propios.

Article 248: 
No list of candidates for elective office may receive from a single source private contributions in excess of the following percentages over their respective expenditure ceilings:
1. Presidential candidates, 3%.
2. Those of deputies, including those of the Central American Parliament, mayors, councilmen and township representatives, 25%.
To apply this ceiling, the list of candidates shall subtract what it finances with its own resources.

Unofficial English translation.

There is a limit on the amount that can be donated to candidates, but it is not mentioned that this limit applies to the candidates themselves.