There is no constraint on how much winter cycling should cost, nor is there any rule that determines as much. It's all going to be a function of how cold you tend to get, what you want to spend, and what is comfortable for you. You can get by on the cheap with long johns under sweat pants and rubber pack boots. Asking "how expensive should winter cycling clothes be?" is like asking "how long is a rope?"
I don't know what I spent on everything everything that I have because I bought a little at a time, and I watched for sales. I also put none of it in a spreadsheet so I could do a cost analysis. As for what I have....
--one pair of bib tights
--one pair of bib knickers
--a pair of leg warmers
--a pair of arm warmers
--3 long sleeve jerseys
--1 mostly non-breathable windproof cycling shell
--1 waterproof breathable cycling jacket
--1 pair of lightweight gloves
--1 pair of heavyweight gloves (whose graph of mass in my house versus time is a heaviside function)
--1 waterproof breathable skullcap
--1 pair of waterproof booties
Most of the stuff I have is from one brand 'cuz that brands kit fits me near perfectly on top and on the bottom. Some of it was inexpensive, and some of it wasn't. My stuff keeps me warm well down into the coldness. At 20°F I'm damned toasty, and the kit could easily take me much lower, likely into the single digits.
I'd say it's a pretty safe assumption that your LBS will not have the lowest cycling clothing options. If you shop wisely online, you can find great deals, especially if your willing to shop in, say, the UK. I get weekly notices about sales from online dealers I've used and liked. You can find good deals also at REI and at MEC (in Canada). You might also check Pricepoint. Performance Bike has some low prices, but IMHO, they sell a fair bit of kack. Nashbar is even cheaper than Performance Bike.
Sadly, since winter is not far off, you're going to find fewer deals than if you'd shopped last spring or over the summer.
When I wear leg warmers, they go under my shorts. Likewise, arm warmers go under my sleeves. My thick skull cap comes down over my ears on the days it's extra cold. Very few online shops will not exchange clothing that is the wrong size. Very few. Every cycling clothing manufacturer that's worth patronizing has sizing charts. Some companies tend toward a Euro fit (i.e., a fit for thin people), and some companies have sizing that is designed for the typical American (clothing for fat, lazy people). Of course, there are varying fits in between those two extremes. Your best option is to find clothes online that fit your budget and tickle your aesthetic taint. You can then ask on this forum or another, if anyone has used clothing and how it as fit versus their size (i.e., did the XL jersey fit the 5'11", 180 lb guy/gal well or not?). Likewise, when asking that question you can also ask how well the kit held up and functioned. That's about the best you're going to be able to do.
