Exactly what Shannon said. Your little guy is coming out of an infant seat into a convertible that he will use until he is 4-6yrs old, depending on what you buy. Sure, you can spend $40 now nad get a Cosco Scenera, which is a great seat, but he will probably outgrow it in height or weight by the time he's 3yrs old. My 2 1/2yr old is *almost* too tall for this seat (its our airplane/travel seat).
To get a seat that will last your child well past his 4th b-day, you will need to spend a bit more. Look for seats that have a higher harness weight and height. The 3-in-1 seats (Eddie Bauer, Cosco Alpha Omega) will ONLY harness to 40lb, then they must be used as a belted booster seat wit hthe harness removed. And they have short top slots, that very top slot is only good in booster mode, so the 2nd to the top is the highest it will get with the harness.
I know its confusing, but please don't refer to consumer reports when considering a carseat. tHey refuse to divulge thier testing results, and last year it came out they tested the seats wrong and had to retract thier findings. They are unreliable.
Basically what you will wnat to look for is a seat that will harness to 50, 55, 65lbs. These seats are....
Evenflo Triumph ADVANCE (Make sure its says ADVANCE $130). This will rear face to 30lbs and forward face to 50lbs, and will fit most 5yr olds. Great seat, easy to find, easy on the pocket book. Will more than likely last you to age 5 or so, when you can then move your child safely to a high back booster seat.
FIsher Price Safe Voyage Deluxe (online only www.albeebaby.com $130) this is the same shell as the Britax Marathon, made BY Britax for fisher price. WIll rear face to 33lbs and forwad face to 55lbs. This seat will fit most 5-6yr olds. My very tall 6yr old still has about an inch in this seat, so it will last you until it expires. GREAT seat for the money.
Britax Marathon, Decathlon, BOulevard ($270) will rear face to 35lbs, forwad face to 65lbs. Will hold most kids to 6-7yrs old, when you can safely move him into a high back booster. This seat is GREAT, it WILL last you until it expires, and when you consider how much you use it, and how long.... the price makes sense. Go to the store, touch the seats, pick them up, play with hte harness, and you'll notice the huge idfference between the Britax and Graco/Cosco/etc.
SUnshine Kids Radian65 ($270 online or at USABaby.com) will rear face to 35lbs and forward to 65lbs. They have a low belt path and are not compatible with many vehicles, so if you go this route make sure you can return it before you buy in case it won't fit. GREAT seat, heavy made of steel, and foldable.
Recaro has the Como and SIgno, but they just had recalls again so I won't recommend them right now.
I know its confusing, but if you choose a seat that will last your child to age 5+, you will get your moneys worth, and spending $200 on a seat doesn't seem as daunting. :)