The most affordable of our options so far is the Ikea Kura bed. It's a low loft bed that could grow with our family. To start Theo could sleep on a mattress on the ground if I'm too nervous to have him sleep up high. Then when he's older he can move to the top bunk and baby 2 can sleep on the bottom. Apartment Therapy already wrote a great article about using the Kura Bed as a bunk bed here.
The main downside I see to this bed right now is that it has quite a large footprint compared to Theo's current crib or Option 1 and Option 2 and I worry about losing precious playing area. If Theo could easily navigate the top bunk we could leave the bottom open for play but I worry that 3 is too young for the top bunk. I hear mixed opinions on 3 year olds and tall beds.