I want to custom order a streetlight, specifically an American Electric ATBX (ATBX P40 MVOLT R3 3K VR NL).
I want to know how much this configuration would cost, and how much a stock new ATBX would cost?

You would have to contact your local Acuity Brands distributor. You can find them by using the distributor locator on the American Electric Lighting website. Pricing is going to vary by location since they are sold through wholesale distribution. The price I get for one might be higher or lower than the price you get. Typically walk in sales are treated as "homeowner" or "retail".

Prices will vary but I suppose you can use the Grainger price as a baseline. Note that Grainger tends to be on the more expensive side for stuff like this so your local Acuity Brands distributor may sell for cheaper.

I paid around $50-70 CAD for new surplus LED Lumec Roadfocus luminaires with similar specs as the ones on Grainger ones (40w/4000lm, 3000K).

Stuff on Grainger is quite overpriced. As far as contacting my local Acuity Brands distributor, I have 2 options for distributors, utility and non-utility. As far as non-utility lighting goes, there are only 6 distributors in the US, and none are even near where I live (the nearest one is Southeast Sales Support in Georgia). But there is a utility distributor in my state (National Transformer Sales) that is in Raleigh.

Would I be able to buy from a utility distributor, or would they not sell to me?

Utility distributor is what you need, to purchase roadway luminaires. Whether they sell to you or not depends on them. Some locations are very strict about that and some are not. You'll have to just call them or email to find out. They should more than likely.

I sent the email asking about non-utility sales. Wish me luck!

Don't be surprised if they quote you a price of an arm and both legs ! Your price will be determined by just how willing the supplier is to deal with you .

Yeah with stuff like this the price can vary widely depending on your relationship with the supplier and how many you order, so large utilities will be a good deal and prices for a one off will be higher.

So far no reply as to whether or not they sell to non-utility customers (I haven't even asked for a quote yet). I am expecting it to be at least over $100, but if it is too crazy, I might try a different distributor and see if they have more reasonable prices.

Yeah, I'd go with one that's know to be willing to sell to the public and have the full ordering code ready for what you're looking for.

https://www.lumen.ca/en/products/18-lighting/02-fixtures/05-outdoor-lighting-fixtures/05-pole-mount-area-lighting
here is one in Quebec canada that lists PRICING on there website and have some HID cobras "available to order"

ACUITY 579000 Cobrahead

CAD $222.30

I got a quote for a similar configuration last December via Graybar and it was about $300.

Well I give up! Almost a month and still no response! I haven't received ANY reply to that email and frankly, I am just done.

I've found a distributor in Raleigh - LiteSource, LLC - that carries Cree luminaires. Their RUL, while it's an area luminaire rather than a roadway luminaire, is available up to 60 watts/9,000 lumens. An optional acrylic refractor or uplight shield is available.

It just depends who you get there. Places like that typically deal with contractors and utility companies that buy in bulk and spend thousands maybe millions of dollars with them every year. So they aren't always very friendly or willing to help private individuals who are just buying maybe a fixture or two from them. They would rather not even spend the time chasing a small sale like that. I work in irrigation wholesale and that's how it works with us as well. We help homeowners who come in and are looking to buy sprinklers for their lawn from us. We don't turn anyone away unless we're busy and have a line of contractors in the store then we would maybe tell the homeowner sorry we simply do not have the time. Because a lot of the time they ask tons of questions and eat up a bunch of our time and sometimes they don't even end up buying anything from us. They only come in for technical advice which is extremely annoying. I was lucky that I was been able to network with a few people who are very friendly who were willing to order me street lights and photocontrols. Just probably need to reach out to another place and you will probably find someone who will help.