M.F.
I'm not sure about high chair brands, but as far as features on a regular high chair, you want to be sure you get one with wheels. We drug ours all over the kitchen, even the house.
We have a couple of friends who used the Fisher price Healthy Care booster as well. It's a perfect combo of high chair and booster. It's nice that it's portable and you can take it along to visit relatives, even take it in a restaurant.
For carseats, the Graco Comfortsport convertible toddler seat is likely one of the least expensive ones. I think we paid $80 for ours at Target. We used this for both our kids and they loved it. (edit) It's true that the harness straps are rather low, but our daughter is in the 10th percentile in size, so she didn't outgrow it til she was nearly 4, and ready for a belt-positioning booster :-). Our son is already too tall for it at 2 1/2, so he's in a regular forward-facing, 5-pt-harness booster now (I believe the Graco Ultra Car Go booster). However, we did love that little Graco convertible seat because it was so easy for them to nap in the car. The Ultra Car Go is also easy to sleep in (it doesn't go rear facing though). When my 4 yr old is tired, she asks to sit in her brother's seat so she can nap.
A lot of people use the Cosco "alpha omega" because it converts all the way to a belt postitioning booster. It can cost twice as much as the Graco though.
On the car seat, I'd buy new, just for safety reasons. Big Lots often has them at super low prices (even the alpha omega for $80!).
On the high chair, you might try local resale shops. You shouldn't have to spend more than $40.