I have not hunted Montana so this is just general info. You may need warmer stuff than what I'm recommending that far North that late.
I like First Lite Aerowool base layers next to skin. This isn't a bad place to spend a little money, they dry pretty fast, wick pretty well, and don't start stinking with sweat very fast.
Next layer out it's hard to beat fleece for your upper body. There are lots of options here. Fleece insulates and dries fast but isn't real wind resistant. For my lower body I like to skip the fleece most times and just go with Kuiu Kenai zip off pants that I don't put on until I'm in my glassing location.
Next layer for the upper body I want a puffy jacket of some kind. Again there are a lot of options here. I would take my Kifaru LPP for a hunt like that. For a budget options I've heard good things about the Costco puffy jackets. For my lower body I go to softshell pants on this layer.
Past that I like a layer for my upper body quieter than rain gear but tougher and more wind proof than a puffy. I don't like it to be heavy, a Sitka Mountain Jacket has been good for me here. It is somewhere between a wind shirt and a softshell, pretty versatile and under a pound. It also saves me from wearing my rain jacket at times.
After that it's rain gear if it's needed.
I don't wear all these layers all the time but I have them with me. I wear as few as I can get away with when walking and add or subtract them as needed. A good baklava, gloves and merino socks are also good. I like Darn Tough socks and pack a spare pair with me almost all the time. Dry socks after a long hike with a long sit expected can really help keep my feet warm.
As far as doing it on a budget keep an eye out on Ebay, classifieds on forums like this, closeout sales, and facebook groups. I put my system together over quite a few years and it's constantly changing, but I did it for around 1/3 of retail price. Camo patterns and brands don't need to match just get good quality layers that work together. When you upgrade an item or find something that doesn't work for you return or sell the old one.