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Marinoni is a Canadian made bicycle and one of the most respected of any of the high end vintage road bicycles of Canadian origin. The bicycle is made from Columbus SL tubing and likely has Campagnolo drop-outs, features which suggest high end quality.
As for value, there are many things that impact
Vintage Bicycle Value, and some of them have little to do with the bike itself. Size, time or year, your marketing skills and location all play a very important part. So...
Determining value will be a hit or miss thing. $50.00 is hardly a serious evaluation, in my mind, but people are certainly entitled to their opinions. For my money, and I am very cheap when it comes to buying bicycles, I would not feel uncomfortable paying $350.00, if I were to keep it for myself. If I were to purchase it to sell, I would want to pay a good deal less - say $200 tops and then hope to be able to get $500.00 for the bike. And, I am pretty certain that, even in my horribly depressed market, I would get it.