I also have a Snoozer carseat, and they are not inexpensive. However, it is one of the best things I have purchased for my girls.
We tried the carseats that kind of hang down from the neck of the seat, and they didn't like those at all.
I highly recommend if you aren't crating her on your car trips now that you at least get a nice car harness (usually around $30) to strap her in for all your trips until you can settle on a carseat that you like.
Here is an example of one:
Pet Car Harness for Small Dogs