We use Cosco seats for my 4 year old and 3 month old. (the Eddie Bauer ones). Around the $100 range, real easy to use (i.e.- get the kids in and out of). They also have good customer support, as I broke the chest clip on one, and they sent a replacement free of charge.
I've been told by our local Sheriff's Dept. to stick with the 5-point harness type. The ones with the front bar aren't as safe.
The main thing is to have it checked out after you get it in. Police/Sheriff/Fire departments usually do this free of charge. Our daughter has a pool noodle under her rear-facing car seat to get the angle right. And don't be afraid to get those belts tight...that's your bundle of joy in there.
Good luck.