I visited Sevilla during Semana Santa and stayed at the Hosteria Dona Lina:
Dona Lina The website lists a double at 54 euros (not including holidays). Overall, I don't think I'd stay there again but it wasn't bad. It's actually an 8 room hotel above a restaurant smack in the heart of the Santa Cruz quarter. The location can't be beat! There is someone at the desk all night and they are very friendly (not much english though if this is an issue for you). My room was clean but very small....I'm not a big person but the shower was so small I couldn't even bend down to shave my legs in the shower. For anyone tall or "large" :o it wouldn't work at all. To be fair, I had a single so perhaps the doubles are more roomy. I felt slightly claustrophic as my "window" just looked down on the restaurant. There's a plexiglass roof in the restaurant but it was kind of strange not knowing what the weather was like outside or what time of day it was.
Other places I've stayed in Sevilla are the Hotel Alcantara which may be a little on the high end of your price range:
http://www.innsofspain.com/hotelview.aspx?h=1147 It's small and is in a great location in the Santa Cruz quarter and is quite modern with IKEA type furniture.
and the Casa de la Juderia - which would be way off the budget option list.
Hope this helps.