B.W.
Hi! I understand needing new seats on a budget. However what you will want to look for in a carseat is a higher harness height and weight. Some seats look great, like the 3-in-1 (eddie Bauer, Alpha Omega) but they are not great seats. Jack of all trades, master of none. THey have short top harness slots (the very top slot can only be used in booster mode) and they make bad boosters, holding the belt too far away from teh childs body. And they only harness to 40lbs, and most children outgrow them in height around age 3, meaning you have to either purchase antoehr seat or unsafely put them in booster seats.
MY advice would be to look into the Fisher Price Safe Voyage Deluxe at www.albeebaby.com. Its $130, freeshipping, and its the same shell as the Britax Marathon. It was made BY Britax FOR Fisher Price. ITs a GREAt seat that will rear face to 33lbs (you want to keep your children rear facing to the rear facing weight limits of the seat, 33/35lbs) and will forward face to 55lbs. The seat WILL last your child the full 6yrs, meaning you will be able to use them until they expire, then safely move your children to high back boosters at age 6 when the seats expire.
If you don't want to order online, look for the Evenflo Triumph ADVANCE. It will rear face to 30lbs, and forwad to 50lbs. It says it will fit most 5yr olds, though its shorter than the Fisher price, Britax ,etc. Its still a GREAT higher weight seat for $130.
A few others are Sunshine Kids Radian65, Britax Marathon, Boulevard, Decathlon, Recaro Como/Signo (Recaro recently had another recall).
I know it seems daunting to spend more than $100 or $200 on a carseat, but when you think about how much you use it, and how important a carseat is, really youcan't put a price tag on it. And if you purchase a higher harness weight/height seat like a Britax or similar, your children will easily be able to use them until the yare 6+yrs old, or until they expire in 6yrs. You WILL get your moneys worth out of them, considering you will use them every day, multiple times a day, for 6yrs....
My almost 6yr old (45lbs, 49'' tall) still fits in our Marathon. He rides in the Britax Regent, and my 2 1/2yr old just went forward facing in the Marathon.