I agree with other posters -- you can get close to Neapolitan using a steel under a good broiler. I position my steel as close as possible, about 2 inches below the broiler element. Then I preheat for about 20-25 mins -- the time it takes for the air temp to reach 550 which causes the broiler element to turn off. In that time, the surface of the steel gets WAY above 500 deg F. I measured mine with an IR thermometer in the low 700's. Not brick-oven, true Neapolitan hot, but still good. After I open the door to launch my pizza, there is a brief cool-down in air temp, and the broiler element goes back on, which is exactly what I want. The pizza cooks in 110 seconds, after which it has a nice spotty char on the bottom and cornicione. The pizza is so close to the element that if it gets a large bubble, it can actually touch the element and get very charred -- but I don't care, I like that!
Your oven might work differently. You may not be able to get as close to the element as I do. If not, try putting the steel on a sheet pan to raise it up. Also, if your broiler cycles on and off, try opening the door to make it kick on. Don't worry about losing hot air -- you are cooking with a preheated steel from below and direct IR radiation from above -- not hot air. And this is why you don't need a long preheat. If you preheat a long time, the steel will achieve thermal equilibrium with the AIR temp, which is only 500-550 F. You want to preheat it using direct IR radiation from the broiler, and that only takes 20 min or so (if your element stays on).