I disagree that you are just paying for the brand name. I have owned both Cosco, Evenflo, and Britax seats, and I will NEVER buy anything but Britax again. The quality is outstanding, the harness doesn't twist, and the seat will accomidate a child up to at least age 5/6 in the 5pt harness. Sure, you can purchase a $40 seat that is just as safe, but chances are your child will outgrow it in height around age 3, long before your child can safely move to a booster, meaning you have to purchase another higher harness weight seat anyway.
That happened to us. We purchased the Cosco Alpha Omega under the guise that it was the 'only seat we'd ever need'.... yeah right! He outgrew it in height by his 3rd b-day, and no 3yr old is mature enough, either physically or mentally, to sit in a belted booster. So we neded up shelling out another $200 for a Britax Marathon to keep him in a 5pt harness. He rode in that seat until he was 4, and our youngest son outgrew the infant seat, and we purchasd yet another Britax, the Regent, for our oldest. He's now 6.5 and still in the Britax Regent, and our 3yr old just went forward facing in the Marathon not long ago.
My point is, you get what you pay for. Yes, the $40 Cosco Scenera is a great cheap seat, but its not padded at all, and it will be outgrown before your child reaches 40lbs, and most likely long before he/she is ready for a belted booster. The higher harness weight seats are more expensive, but you'll be able to use them at least 3yrs beyond the cheaper lower weight seats.... and keeping your child in a 5pt harness is the most important!
Spend the money now, purchase a higher harness weight seat like the Britax Marathon, Sunshine Kids Radian65, Evenflo Triumph ADVANCE. You'll spend $200-$250 now, but your child will be in this seat until he's 6yrs old, meaning you will get the full 6yr life out of the seat before it expires, and then you can purchase a simple booster until your child is 8yrs/80lbs and can sit in the adult seatbelt without a carseat/booster.