Seville hotel rates are really high if you hit dates around Easter, so timing matters a lot.
For stays during Holy Week in Cadiz and with 2 of 6 nights falling during Holy Week in Seville, I am paying 80 euros per night for a single room. I chose about the least expensive place I could find in a convenient location that had a vacancy as of early January. By comparison, I am paying nightly rates of 41 euros in Ubeda, 45 euros in Cordoba, 29 euros in Ronda, 56 euros in Malaga and 39 euros in Granada. Those are for stays in April or early May that do not touch Holy Week.
You're smart to be working on this early; I think it will give you a better chance of getting a good-value deal during Holy Week. Now, the bit about quiet--well, that can be tricky. I'd read a bunch of reviews on booking.com if the property is listed there. (You don't have to make the reservation through booking.com.) Remember that Spaniards eat dinner extremely late. It is common for diners to return home or to their lodgings between midnight and 1 AM. Not only will there be people on the street, they may be heading for the room next to yours in the hotel. Take earplugs. It never hurts to request a quiet room, but be aware that quiet often means no view, unless you count an airshaft. [Edited to add] Remember, I was in single rooms; they tend to be in odd corners. Maybe all the airshaft views are in the single rooms!