What country are you from?
I believe the maxi-cosi and the
comfort sport have low harness slots. That in turn would be outgrown sooner than your son will be ready for a
booster. The Eddie Bauer 3 in 1 is not a good seat. It is also outgrown too soon. It is not good as a
booster seat either.
I hear the roundabouts are good seats, but has a 40lb weight limit and shorter slots than the blvds. So if you buy it you would end up buying another seat in the future.
If price is the main issue, why dont you consider the Evenflo Triumph Advance, or even the Fisher Price Safe Voyage which by the way is manufactured by
Britax for Fisher Price.
I really hope you visit
Car Seat.Org - Carseat, Vehicle & Child Passenger Safety Forums like I said, there are alot of people on that site that would be willing to share their knowledge.