If a person may make an offering for a candle to burn before the statue of a saint or the Blessed Virgin, why not before the Blessed Sacrament? If someone wanted to pay the cost of the hosts or wine to be used in the Eucharist, would that be wrong? Or if a person donated a chalice, would that be wrong? Then why not an offering for the sanctuary light?
Parishes are generally eager to welcome donations and Catholics are encouraged to support their parishes as well as they can.