It's been years since we bought our gas fireplace and we got it installed with a removable glass front, not doors. You don't want to scrimp on fireplace doors because the doors have to be able to withstand the heat of the fireplace without shattering. DSis's fireplace doors shattered, very luckily, no one was injured.
We just paid somewhere around $150 for a pretty small piece of glass for our pellet stove- I guess the glass is special for fires and very pricey.....we got ours from the stove manufacturer.