I agree with the vintage Japanese bikes, they were fantastically made. But as all bike companies they had their low end bombs so it would behoove you to do a lot of internet reading on the various brands and their models and the components they offered. Fuji is another serious consideration, in fact I rank Miyata from models 510 on up (higher the number the better the bike to they get to Team-their top of the line) with the triple butted splined tubing, followed by Fuji with the Valite Quad butted tubing, as the best frames that came out of Japan. Those frames are very responsive frames and will last forever. Fuji for some reason rated their bikes heavier then they really were, I have a 58cm 1988 Fuji Club that according to the catalog weighs 23 pounds, mine weighs 20.8 pounds and it's all original so I've done nothing to lighten it up. This Fuji I bought this last spring, it had 5 miles on it, it's in excellent condition and it cost me $100 through CraigsList. You do need some patience going through Craigslist because most people are trying to rip people off on the vintage factor. I saw a 1982 Motebecane Record Sport, a cheap low end bike with a poser name, in fair condition and the guy wanted $600! He's looking for the fool who knows nothing about vintage bikes. Others won't have a clue as to what they have and well sell them cheap, those are the guys your looking for.
Treks can also sometimes be found for reasonable prices, any model with a 400 designation or higher are great bikes, made in America but used mostly Ishawata or Reynolds tubing. See this for extensive info on Treks:
Vintage Trek - A brief history of Trek Bicycle Corporation and its steel bike frames
Any bike that comes with the dual brake levers, one for activation at the hoods or drops and another bar that's used for activation when on the bar tops is a good indication the bike is a lower end bike, stay away from those.
There are archived catalogs available on line for a lot of brands, these will have a wealth of information. Here's a few catalogs I found because I own these bike brands:
Miyata:
Miyata Bicycle Catalogs
Fuji:
Fuji Models to Thumbnails
Schwinn:
Schwinn Years by Model
I do not own a Panasonic but they had some really nice bikes that were highly under rated; here's some info on those:
Panasonic Bicycle Ads from the past… | Panasonic Bicycles Virtual Museum
I disagree with the Varsity. I was a teenager when those came out new and they were junk when they were new, plus they weighed 45 pounds! Sure the frames were tough but the components were crappy. And because the baby boomers are trying to buy back our youth and the Varisty figures into that equation as a popular culture bike thing back then, people are selling them for way more then their worth at between $100 to $250! There not worth their scrap value!!! sorry, just my opinion.
