Sorry- this may be a little long!
I will start by offering this website: http://www.aap.org/family/carseatguide.htm has every carseat sold in the US listed at the bottom with the height/weight safety guidlines for each. That could help narrow your search. It also has aproximate price of each seat- Very helpful!
Now- I am a HUGE Britax fan! It is the only brand that my son has used other than the carrier kind. They are the top of the line for safety marks and comfort for the child. When DS out grew his Roundabout (convertable that goes to 40 lbs) at 26 M, all the seats I could find for "Forward facing youth seats" only used harness to 40 lbs, then dropped to belt positioning shoulder restraint. At TWO YEARS OLD, I was NOT ready to use the car seat buckle! We found the Britax Regent at that point. It goes to 80lbs and 4'5" always in 5 point harness. I liked the assurance that he would not outgrow it physically before I was ready to let him drop to one of those $40-$50 boosters. He is 3y 4m now and still does not complain obout getting "buckeled up" in his seat. 5 points is MUCH safer than a regular belt booster. So- overall, my advice would be buy the Regent as his everyday seat, and move the convertable to the extra car. I know that is about 3 times what you wanted to spend, but even if CA goes to the 8 years/80 lbs car seat law (which they are gearing up for) his seat will serve him all the way through.
If $$ Britax is not an option, use the site I gave you to see what seats do fit what you NEED in the seat at the $$ you can afford.