merlincycles.com has the Veloflex Roubaix for $68, the Arenberg for 73, the Vlaaderen for 91. Not exactly cheap but you aren't likely to find cheaper unless you get lucky on ebay. When you first open site you may see prices quoted in pounds sterling, when you get to the tires you'll see $$ and note that prices include shipping. Or they include shipping if you meet minimum order of 50 pounds, which is currently about one Veloflex Roubaix.
The Servizio Corse, if you have the 3/$50 version, work a lot better for lighter riders. Since they are narrow you have to pump them pretty high. If you are heavy and need over 120psi (or over 140psi) they won't take it for long.