Seville is not an expensive city to visit considering that most attractions have low entry prices compared to bigger cities, and accommodation costs are also low. Transport is more or less free as you will end up walking around in a compact area which has the main attractions.
Many Seville attractions like the Alcazar and Cathedral can be visited for free if you plan your visit in advance. The Spanish Inquisition museum in Triana is free for all visitors; so is the fine arts museum. Top class Flamenco performances can also be watched for free if you know where to go. Other free attractions in Seville are Maria Luisa Park and Plaza de Espana.