You are correct -- Virtuoso certainly targets high-end properties. That's why when looking at Starwood properties (of which there are nearly 1,000 worldwide), less than 40 appear to be Virtuoso. However, that is not to say that Virtuoso properties are not affordable. For example, I've seen Virtuoso rates at the Nines (in Portland; it gets great reviews in the Starwood forum) for just a little over $100 for a few months now.

At this point, I don't know of any way to book Virtuoso rates on-line (unless you consider e-mailing an agent as booking on-line). There was a thread recently that talked about a site that is partnered with a similar program called Signature that allows online bookings: www.whatahotel.com.