Just thought I'd jump in. I don't have a RAV4, but I have a Ford Focus, which is also on the narrow side and there's not much leg room in the back seat.
I have a radian in the middle seat for dd1 who is 43" tall and 40 lbs (seatbelt install) and a Chicco Keyfit 22 in the outboard passenger side. I am able to fit a forward facing Britax Marathon in the other outboard seat when needed for her shorter friends. I can also fit it rearfacing...just not fully reclined to 45 degrees, which will be fine for dd2 when she outgrows her chicco bucket seat.
I chose the Keyfit because it fit better than a Snugride...namely in how the base installed very securely (it was narrower and easier the adjust) and how there seemed to be more space between the chicco and the front passenger seat (I can ride comfortably in front) than there was with the Snugride. Also the Chicco bucketseat carrying handle can be in the upright position while travelling in the car - a BIG factor in how well it fits behind our front seats.
I tried a Britax Frontier in the car, thinking it might fit beside the Radian and the Keyfit....and there was NO WAY it would fit. The Boulevard might be a different story though?
Buying a Radian is still cheaper than a Minivan! However, safety is so many factors....and the vehicle itself is a big factor too. Minivans and SUV's both have the issue of flying cargo and need some sort of cargo net or guard to prevent your groceries from becoming missiles in an accident.
Good luck :-)