Mary Ann, for the dimensions that I recommend, Baking Steel would be in the $150+ realm.
Baking Steel's default sizes are way too small for NY style. When you get into pizzas that small, they're all rim. You want to biggest square plate your oven can accommodate- touching the back wall and almost touching the door.
From looking at the specs of your oven, it looks like your shelves are 17.25 x 22.75. There's usually a small gap between the shelves and the door, so there's a chance you can fit an 18" plate. For NY, there's nothing more magical than an 18" pizza.
When sizing the steel plate, you'll want to measure the living daylights out of that space. You can't be too careful at this stage. Make a cardboard dummy, put it in place and see if the door closes. Be acutely aware of lips on the back of the shelf, the position of the convection fan, along with protrusions on the door. Put a piece of paper on the cardboard, extending out the oven a bit and, when you close the door, see how far it pushes back. You'll want to size the plate so that the door, when closed, just clears it, with absolutely no additional space.
Hot rolled (aka 'mild' aka a36) steel is what you want. I was, for a while, recommending 3/4", but, other than for better recovery for very large parties (more than 10 pizzas baked back to back), I no longer recommend it. 1/2" is the one to go with, and, for easier installing, you want to get it split down the middle lengthwise (see photo below) If you know someone that deals in plate, great, otherwise, unless you want to spend $150+, do a search for 'yourtown, state steel' in google maps (see photo below) and just start making calls.