Off-campus housing in Eugene can be convenient and cheap, depending on how far off campus you're willing to look. The vast majority of student housing is found in the many apartment complexes located near Autzen Stadium, across from the Willamette River (roughly a 10-minute drive from campus). University Commons, Ducks Village, and Chase Village all offer newer apartments at reasonable prices and try to cater to student needs. If you don't have a car, the bus system is really convenient. Although it's a bit of a walk from campus, the LTD bus line runs frequently near all apartments and is free to students. These students usually tend to stay in this area beacuse of its distance. This can be a great way of bonding but can feel a little secluded at times as well.
As far as housing within a short walk of campus, it's hit or miss. Several houses and apartment complexes are located just a few blocks from UO, though their prices vary greatly. Apartments close to campus tend to run the same price as apartments by Autzen, but they are more confined and have fewer amenities. If you want housing for the fall, you'll need to start looking in the spring, preferably early. Everything will have filled up by the time summer rolls around, and you'll have a lot of trouble finding anywhere to live. In general, prices tend to be reasonable and cheaper than living in the dorms. Although it's a little less convenient than being on campus constantly, the freedom that comes along with your own apartment will make it worthwhile, especially in your later years at the University.