Rather than go to a local music store, your best bet is to first go on-line and then contact an early music specialty shop. Several come to mind: http://www.lazarsearlymusic.com
The reason I suggest this is because local shops will likely either not stock recorders at all, or else their offerings might only be the most inexpensive “school” sopranos.
That said, not every early music specialty shop will offer every brand of decent plastic alto recorders. And, while not every shop will want to discuss plastic recorders with you over the phone, the ones who will discuss them with you over the phone will be self-evident.
A common procedure is for people to get a shipment of a few different wood recorders sent to them to try before they buy. However, this is probably neither necessary with plastic nor would it be cost effective since the recipient of the shipment would have to pay return postage.
So, after you have done your on-line reading and watching Sarah’s videos, call the most promising looking shop and discuss plastic recorders with them. If you spend a few minutes on the phone with them, and end up purchasing their top-of-the-line plastic alto, you can’t go wrong.