22. Is there a limit on in-kind donations to candidates?

Source 1: Article 64, paragraph 1, Political Parties Act 2013.

Artículo 64 inciso 1°. – Las contribuciones privadas solo pueden acreditarse a favor de los partidos políticos.

Article 64, paragraph 1. – Private contributions can only be credited to political parties.

Source 2: Article 10, paragraph 1, Provisions for the Nomination of Non-Party Candidates in
the 2010 Legislative Elections

Artículo 10 inciso 1°.- El candidato no partidario podrá recibir donaciones de fuentes privadas, para lo cual abrirá una cuenta bancaria única a su nombre o del Grupo de Apoyo que lo respalda. Adicionalmente el candidato deberá llevar un libro de contabilidad formal autorizado por el Tribunal donde se registren los ingresos y egresos totales, así como las donaciones en especie que reciba, los cuales deberán liquidarse al final del proceso electoral, todo lo cual servirá para fiscalizar el origen y uso lícito de los fondos.

Article 10, paragraph 1. – Non-party candidates may receive donations from private sources, for which purpose
they shall open a single bank account in their name or in the name of the Support Group backing them. In addition, the
candidate must keep an official accounting book authorized by the Court, where they shall record
total income and expenses, as well as any donations in kind received, which must be settled
at the end of the electoral process, all of which will serve to monitor the origin and lawful use of the funds.

Ley de Partidos: https://www.asamblea.gob.sv/sites/default/files/documents/decretos/2E597B83-D1C9-4C91-A9C9-6EC8A44FBA0F.pdf 
Regulación candidaturas no partidarias: https://www.asamblea.gob.sv/sites/default/files/documents/decretos/45E06ECC-27EC-49EC-B5D5-5D29814BAD32.pdf  

This only applies to non-party candidates, as the regulations do not set any limits. In the case of party candidates, it does not apply because the law establishes that only parties may receive contributions.
In fact, by not regulating the financing activities of party candidates, the law creates a loophole that is exploited in practice by candidates to raise funds without being accountable to their parties or the electoral authority for the origin and destination of the funds received.