Wood I beams cannot be used for a structural beam. Are you thinking of laminated beams (lam beams in the trade), parallel strand, orientated strand, or one of the other engineered beams. All of them will work, but generally wood will require a deeper depth of beam than steel, sometimes the deciding factor if headroom is crucial. Even though budget is a concern, I would not replace basement load bearing walls without the advice of an engineer. They were put there for a reason, and may have quite substantial loads on them , possibly transferred all the way from the roof. No one wants to pay an engineer, but his fee will be very modest compared to the possible damage from creating a structural faux pax.